Optical subcarrier dual-path protection and restoration for optical communications networks

ABSTRACT

An example system includes a first network device having first circuitry. The first network device is configured to perform operations including receiving data to be transmitted to a second network device over an optical communications network, and transmitting first information and second information to the second device. The first information is indicative of the data, and is transmitted using a first communications link of the optical communications network and using a first subset of optical subcarriers. The second information is indicative of the data, and is transmitted using a second communications link of the optical communications network and using a second subset of optical subcarriers. The first subset of optical subcarriers is different from the second subset of optical subcarriers.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/US2020/055107, filed Oct. 9, 2020, which claims the benefit of U.S.Provisional Patent Application No. 62/913,253, filed Oct. 10, 2019,which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

This disclosure relates to optical communications networks.

BACKGROUND

In an optical communications network, network nodes (e.g., computerdevices) can exchange information using one or more of optical links(e.g., lengths of optical fiber) extending between them. For example, afirst network node and a second network node can be interconnected byone or more optical links. The first network node can transmit data tothe second network node by generating an optical signal, modulating theoptical signal based on the data (e.g., using one more opticalsub-carriers), and transmitting the optical signal over the one or moreoptical links. The second node can demodulate the optical signal torecover the data.

However, in some cases, one or more of the optical links of an opticalcommunications network may be severed or otherwise rendered inoperable.For example, an optical link may be physically severed (e.g., due to a“fiber cut”), such that it cannot convey optical signals from one end ofthe optical link to the other. As another example, an optical linkand/or the equipment coupled along the optical fibers (e.g., “linesystem components”) may be misconfigured or experience a malfunction,such that optical signals are not conveyed accurately (or not conveyedat all) through the optical communications network. Accordingly, theconnectivity between nodes of the optical communications network may beinterrupted, and the reliability of the communications network may bedegraded.

SUMMARY

In an aspect, a system includes a first network device having firstcircuitry. The first network device is configured to perform operationsincluding receiving data to be transmitted to a second network deviceover an optical communications network; and transmitting, to the seconddevice: first information indicative of the data using a firstcommunications link of the optical communications network, where thefirst information is transmitted using a first subset of opticalsubcarriers, and second information indicative of the data using asecond communications link of the optical communications network, wherethe second information is transmitted using a second subset of opticalsubcarriers, and where the first subset of optical subcarriers isdifferent from the second subset of optical subcarriers.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, the first information and the secondinformation can be identical.

In some implementations, the first information can be different from thesecond information.

In some implementations, the first communications link and the secondcommunications link can form at least a portion of a communications ringthat communicatively interconnects the first network device and thesecond network device.

In some implementations, the first subset of optical subcarriers can beselected from a plurality of optical subcarriers allotted to the firstnetwork device.

In some implementations, the optical subcarriers of the first subset ofoptical subcarriers can be associated with respective frequencies thatare contiguous with one another in a frequency domain.

In some implementations, the second subset of optical subcarriers can beselected from the plurality of optical subcarriers allotted to the firstnetwork device.

In some implementations, the optical subcarriers of the second subset ofoptical subcarriers can be associated with respective frequencies thatare contiguous with one another in a frequency domain.

In some implementations, the first subset of optical subcarriers can beassociated with one or more first frequencies. The second subset ofoptical subcarriers can be associated with one or more secondfrequencies. In some implementations, the one or more first frequenciesare not contiguous with the one or more second frequencies in afrequency domain.

In some implementations, the first subset of optical subcarriers can beassociated with one or more first frequencies, the second subset ofoptical subcarriers can be associated with one or more secondfrequencies, and one or more additional optical subcarriers can beassociated with one or more additional frequencies. The one or moreadditional frequencies can be disposed between the one or more firstfrequencies and the one or more second frequencies in a frequencydomain.

In some implementations, the first subset of optical subcarriers can beassociated with one or more first frequencies, and the second subset ofoptical subcarriers can be associated with one or more secondfrequencies. The one or more first frequencies and the one or moresecond frequencies can be separated from one another by one or moreadditional frequencies in a frequency domain.

In some implementations, a number of optical subcarriers in the firstsubset of optical subcarriers can be the same as a number of opticalsubcarriers in the second subset of optical subcarriers.

In some implementations, a number of optical subcarriers in the firstsubset of optical subcarriers can be different from a number of opticalsubcarriers in the second subset of optical subcarriers.

In some implementations, the first network device can be configured totransmit the first information and the second information by modulatingan output of a laser to generate a modulated optical signal includingthe first subset of optical subcarriers and the second subsets ofoptical subcarriers; providing the modulated optical signal to anoptical splitter; splitting the modulated optical signal into a firstportion and a second portion, where each of the first portion and thesecond portion includes the first subset of optical subcarriers and thesecond subset of optical subcarriers; selecting the first subset ofoptical subcarriers from the first portion of the modulated opticalsignal; selecting the second subset of subcarriers from the secondportion of the modulated optical signal; transmitting the first subsetof optical subcarriers to the second network device using the firstcommunications link; and transmitting the second subset of opticalsubcarriers to the second network device using the second communicationslink.

In some implementations, the first network device can be configured toselect the first subset of optical subcarriers by selecting the firstsubset of optical subcarriers with a wavelength selective switch.

In some implementations, the first network device can be configured toselect the second subset of optical subcarriers by selecting the secondsubset of optical subcarriers with the wavelength selective switch.

In some implementations, the first network device can include one ormore hub network devices. The second network device can include one ormore leaf network devices.

In some implementations, each of the optical subcarriers in the firstsubset of optical subcarriers and the second subset of opticalsubcarriers can be a respective Nyquist subcarrier.

In another aspect, a system includes a first network device having firstcircuitry and a second network device having second circuitry. The firstnetwork device and the second network device are configured to performoperations including receiving, by the first network device and thesecond network device, data to be transmitted to a third network deviceover an optical communications network; transmitting, by the firstnetwork device to the third network device, first information indicativeof the data using a first communications link of the opticalcommunications network, where the first information is transmitted usinga first subset of optical subcarriers; and transmitting, by the secondnetwork device to the third network device, second informationindicative of the data using a second communications link of the opticalcommunications network, where the second information is transmittedusing a second subset of optical subcarriers, and where the first subsetof optical subcarriers is different from the second subset of opticalsubcarriers.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, the first information and the secondinformation can be identical.

In some implementations, the first information can be different from thesecond information.

In some implementations, the first communications link and the secondcommunications link can form at least a portion of a communications ringthat communicatively interconnects the first network device, the secondnetwork device, and the third network device.

In some implementations, the first subset of optical subcarriers can beselected from a plurality of optical subcarriers allotted to the firstnetwork device.

In some implementations, the optical subcarriers of the first subset ofoptical subcarriers can be associated with respective frequencies thatare contiguous with one another in a frequency domain.

In some implementations, the second subset of optical subcarriers can beselected from the plurality of optical subcarriers allotted to the firstnetwork device.

In some implementations, the optical subcarriers of the second subset ofoptical subcarriers can be associated with respective frequencies thatare contiguous with one another in a frequency domain.

In some implementations, the first subset of optical subcarriers can beassociated with one or more first frequencies, and the second subset ofoptical subcarriers can be associated with one or more secondfrequencies. In some implementations, the one or more first frequenciesare not contiguous with the one or more second frequencies in afrequency domain.

In some implementations, the first subset of optical subcarriers can beassociated with one or more first frequencies, the second subset ofoptical subcarriers can be associated with one or more secondfrequencies, and one or more additional optical subcarriers can beassociated with one or more additional frequencies. The one or moreadditional frequencies can be disposed between the one or more firstfrequencies and the one or more second frequencies in a frequencydomain.

In some implementations, the first subset of optical subcarriers can beassociated with one or more first frequencies, and the second subset ofoptical subcarriers can be associated with one or more secondfrequencies. The one or more first frequencies and the one or moresecond frequencies can be separated from one another by one or moreadditional frequencies in a frequency domain.

In some implementations, a number of optical subcarriers in the firstsubset of optical subcarriers can be the same as a number of opticalsubcarriers in the second subset of optical subcarriers.

In some implementations, a number of optical subcarriers in the firstsubset of optical subcarriers can be different from a number of opticalsubcarriers in the second subset of optical subcarriers.

In some implementations, the first network device can be configured totransmit the first information by modulating an output of a first laserto generate a first modulated optical signal including the first subsetof optical subcarriers; and transmitting the first modulated opticalsignal to the third network device using the first communications link.

In some implementations, the second network device can be configured totransmit the second information by modulating an output of a secondlaser to generate a second modulated optical signal including the secondsubset of optical subcarriers; and transmitting the second modulatedoptical signal to the third network device using the firstcommunications link.

In some implementations, each of the first network device and the secondnetwork device can include one or more hub network devices, and thethird network device can include one or more leaf network devices.

In some implementations, each of the optical subcarriers in the firstsubset of optical subcarriers and the second subset of opticalsubcarriers can be a respective Nyquist subcarrier.

In another aspect, a system includes a first network device having firstcircuitry. The first network device is configured to perform operationsincluding receiving data to be transmitted to a second network deviceover an optical communications network; transmitting, to the seconddevice, first information indicative of the data using a firstcommunications link of the optical communications network, where thefirst information is transmitted using a first subset of opticalsubcarriers; determining a fault in the first communications link; andresponsive to determining the fault in the first communications link,transmitting, to the second network device, second informationindicative of the data using a second communications link of the opticalcommunications network, where the second information is transmittedusing a second subset of optical subcarriers, and where the first subsetof optical subcarriers is different from the second subset of opticalsubcarriers.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, the first network device can be configured todetermine the fault in the first communications link by determining thatan optical fiber of the first communications link has been severed.

In some implementations, the first network device is configured todetermine the fault in the first communications link by determining thata line system component of the first communications link ismalfunctioning.

In some implementations, the first information and the secondinformation can be identical.

In some implementations, the first information can be different from thesecond information.

In some implementations, the first communications link and the secondcommunications link can form at least a portion of a communications ringthat communicatively interconnects the first network device and thesecond network device.

In some implementations, the first subset of optical subcarriers can beselected from a plurality of optical subcarriers allotted to the firstnetwork device.

In some implementations, the optical subcarriers of the first subset ofoptical subcarriers can be associated with respective frequencies thatare contiguous with one another in a frequency domain.

In some implementations, the second subset of optical subcarriers can beselected from the plurality of optical subcarriers allotted to the firstnetwork device.

In some implementations, the optical subcarriers of the second subset ofoptical subcarriers can be associated with respective frequencies thatare contiguous with one another in a frequency domain.

In some implementations, the first subset of optical subcarriers can beassociated with one or more first frequencies, and the second subset ofoptical subcarriers can be associated with one or more secondfrequencies. In some implementations, the one or more first frequenciesare not contiguous with the one or more second frequencies in afrequency domain.

In some implementations, the first subset of optical subcarriers can beassociated with one or more first frequencies, the second subset ofoptical subcarriers can be associated with one or more secondfrequencies, and one or more additional optical subcarriers can beassociated with one or more additional frequencies. The one or moreadditional frequencies can be disposed between the one or more firstfrequencies and the one or more second frequencies in a frequencydomain.

In some implementations, the first subset of optical subcarriers can beassociated with one or more first frequencies, and the second subset ofoptical subcarriers can be associated with one or more secondfrequencies. The one or more first frequencies and the one or moresecond frequencies can be separated from one another by one or moreadditional frequencies in a frequency domain.

In some implementations, a number of optical subcarriers in the firstsubset of optical subcarriers can be the same as a number of opticalsubcarriers in the second subset of optical subcarriers.

In some implementations, a number of optical subcarriers in the firstsubset of optical subcarriers can be different from a number of opticalsubcarriers in the second subset of optical subcarriers.

In some implementations, the first network device can include one ormore hub network devices, and the second network device can include oneor more leaf network devices.

In some implementations, each of the optical subcarriers in the firstsubset of optical subcarriers and the second subset of opticalsubcarriers can be a respective Nyquist subcarrier.

In another aspect, a system includes a first network device includingfirst circuitry. The first network device is configured to performoperations including monitoring for incoming optical signals on a firstcommunications link and a second communications link of an opticalcommunications network, where each of the first communications link andthe second communications link communicatively interconnects the firstnetwork device and a second network device; receiving, by the firstnetwork device, at least one of: a first signal including firstinformation indicative of data transmitted by the second network deviceusing the first communications link and using a first subset of opticalsubcarriers, or a second signal including second information indicativeof the data transmitted by the second network device using the secondcommunications link and using a second subset of optical subcarriers,where the first subset of optical subcarriers is different from thesecond subset of optical subcarriers; and retrieving, by the firstnetwork device, the data from at least one of the first signal or thesecond signal.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, the first network device can be furtherconfigured to perform at least one of: transmitting the data to a thirdnetwork device, or transmitting the data to the third network device.

In some implementations, the first communications link and the secondcommunications link can form at least a portion of a communications ringthat communicatively interconnects the first network device and thesecond network device.

In some implementations, the optical subcarriers of the first subset ofoptical subcarriers can be associated with respective frequencies thatare contiguous with one another in a frequency domain.

In some implementations, the optical subcarriers of the second subset ofoptical subcarriers can be associated with respective frequencies thatare contiguous with one another in the frequency domain.

In some implementations, the first frequencies are not contiguous withthe second frequencies in the frequency domain.

In some implementations, one or more additional optical subcarriers canbe associated with one or more additional frequencies, and the one ormore additional frequencies can be disposed between the one or morefirst frequencies and the one or more second frequencies in thefrequency domain.

In some implementations, the first subset of optical subcarriers can beassociated with one or more first frequencies, and the second subset ofoptical subcarriers can be associated with one or more secondfrequencies. The one or more first frequencies and the one or moresecond frequencies can be separated from one another by one or moreadditional frequencies in the frequency domain.

In some implementations, a number of optical subcarriers in the firstsubset of optical subcarriers can be the same as a number of opticalsubcarriers in the second subset of optical subcarriers.

In some implementations, a number of optical subcarriers in the firstsubset of optical subcarriers can be different from a number of opticalsubcarriers in the second subset of optical subcarriers.

In some implementations, wherein the first network device can beconfigured to retrieve the data from at least one of the first signal orthe second signal by determining that the first signal was not receivedfrom the second network device; determining that the second signal wasreceived from the second network device; and responsive to determiningthat the first signal was not received from the second network deviceand determining that the second signal was received from the secondnetwork device, retrieving the data from the second signal.

In some implementations, the first network device can be configured tomonitor for incoming optical signals on the first communications linkand the second communications link by tuning a receiver of the firstnetwork device to one or more first frequencies associated with thefirst subset of optical subcarriers, and responsive to determining thatthe first signal was not received from the second network device, tuningthe receiver of the first network device to one or more secondfrequencies associated with the second subset of optical subcarriers.

In some implementations, the first network device can be configured toretrieve the data from at least one of the first signal or the secondsignal can include determining that the first signal was received fromthe second network device; determining one or more first quality metricsassociated with the first signal; determining that the second signal wasreceived from the second network device; determining one or more secondquality metrics associated with the second signal; and retrieving, basedon the one or more first quality metrics and the one or more secondquality metrics, the data from one of the first signal or the secondsignal.

In some implementations, at least one of the one or more first qualitymetrics can include an indication of a latency associated with atransmission of the first signal using the first communications link.

In some implementations, at least one of the one or more first qualitymetrics can include an indication of a pre-forward error correctionquality factor (pre-FEC Q) associated with a transmission of the firstsignal using the first communications link.

In some implementations, at least one of the one or more second qualitycan include an indication of a latency associated with a transmission ofthe second signal using the second communications link.

In some implementations, at least one of the one or more second qualitycan include an indication of a forward error correction quality factor(pre-FEC Q) associated with a transmission of the second signal usingthe second communications link.

In some implementations, the first network device can include one ormore hub network devices, and the second network device can include oneor more leaf network devices.

In some implementations, each of the optical subcarriers in the firstsubset of optical subcarriers and the second subset of opticalsubcarriers can be a respective Nyquist subcarrier.

In another aspect, an apparatus includes a digital signal processor thatis operable to receive information signals including plurality of bitsof information and provide a plurality of digital signals based on theinformation signals; digital-to-analog conversion circuitry operable toreceive the digital signals from the digital signal processor andprovide a plurality of analog signals based on the digital signals;driver circuitry operable to output drive signals based on the analogsignals; a laser operable to provide an optical signal; and an opticalmodulator operable to modulate at least a portion of the optical signalbased on the drive signals to provide a modulated optical signal. Themodulated optical signal includes a first group of optical subcarriersand a second group of optical subcarriers. The first group of opticalsubcarriers includes a first optical subcarrier and the second group ofoptical subcarriers includes a second optical subcarrier. The firstoptical subcarrier carries first data and the second optical subcarriercarries second data. The first and second data are indicative of theplurality of bits of information.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, the first data can be the same as the seconddata.

In some implementations, a guard band can spectrally separate firstfrequencies associated with the first group of optical subcarriers fromsecond frequencies associated with the second group of opticalsubcarriers.

In some implementations, the apparatus can include an optical splitter.The splitter can have an input and first and second outputs. The inputcan be operable to receive the modulated optical signal. The firstoutput can be operable to supply a first portion of the modulatedoptical signal. The second output can be operable to supply a secondportion of modulated optical signal.

In some implementations, the first portion of the modulated opticalsignal can be a first power-split portion of the modulated opticalsignal and the second portion of the modulated optical signal can be asecond power-split portion of the modulated optical signal.

In some implementations, the apparatus can include a wavelengthselective switch that receives the first portion of the modulatedoptical signal.

In some implementations, the apparatus can include a first wavelengthselective switch that receives the first portion of the modulatedoptical signal; and a second wavelength selective switch that receivesthe second portion of the modulated optical signal.

In some implementations, the first wavelength selective switch cansupply the first group of optical subcarriers to a first opticalcommunication path including a first optical fiber and the secondwavelength selective switch can supply the second group of opticalsubcarriers to a second optical communication path including a secondoptical fiber.

In some implementations, each optical subcarrier in the first group ofoptical subcarriers can be a Nyquist subcarrier.

In some implementations, the apparatus can include a wavelengthselective switch that receives the first portion of the modulatedoptical signal and the second portion of the modulated optical signal.

In some implementations, the wavelength selective switch can supply thefirst group of optical subcarriers to a first optical communication pathincluding a first optical fiber, and the wavelength selective switch cansupply the second group of optical subcarriers to a second opticalcommunication path including a second optical fiber.

In some implementations, the apparatus can include an optical splitter.The optical splitter can receive the optical signal from the laser andsupply said at least a portion of the optical signal to the modulator.

In another aspect, an apparatus includes a polarization beam splitterthat is operable to receive a modulated optical signal. The modulatedoptical signal includes a plurality of optical subcarriers. Themodulated optical signal includes a first group of optical subcarriersand a second group of optical subcarriers, The first group of opticalsubcarriers includes a first optical subcarrier and a second opticalsubcarrier. The second group of optical subcarriers includes a thirdoptical subcarrier and a fourth optical subcarrier. The first opticalsubcarrier carries first data and the second optical subcarrier carryingsecond data. The third optical subcarrier carries third data and thefourth optical subcarrier carrying fourth data. The first data isindicative of a first plurality of bits of information and the thirddata is indicative of the first plurality of bits of information. Thesecond data is indicative of a second plurality of bits of informationand the fourth data is indicative of the second plurality of bits ofinformation. The apparatus also includes optical hybrid circuitryoperable to receive outputs from the polarization beam splitter andsupply a plurality of optical mixing products; photodetector circuitryoperable to supply electrical signals based on the plurality of opticalmixing products; analog-to-digital conversion circuitry operable toprovide digital signals based on the electrical signals; and a digitalsignal processor operable to output the first plurality of bits ofinformation and the second plurality of bits of information based ondigital signals.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, the first data can be the same as the thirddata.

In some implementations, a guard band can spectrally separate firstfrequencies associated with the first group of optical subcarriers fromsecond frequencies associated with the second group of opticalsubcarriers.

In some implementations, the apparatus can include an optical combinerhaving a first input that receives a first portion of the modulatedoptical signal and a second input that receives a second portion of themodulated optical signal. The first portion of the modulated opticalsignal can include the first plurality of optical subcarriers and thesecond portion of the modulated optical signal can include the secondplurality of optical subcarriers. The optical combiner can have anoutput that supplies the modulated optical signal.

In some implementations, the apparatus can include a first wavelengthselective switch operable to be coupled to a first optical communicationpath including a first optical fiber. The first wavelength selectiveswitch can be operable to receive the first portion of the modulatedoptical signal from the first optical communication path and supply thefirst portion of the modulated optical signal to the first input of theoptical combiner. The apparatus can also include a second wavelengthselective switch operable to be coupled to a second opticalcommunication path including a second optical fiber. The secondwavelength selective switch can be operable to receive the secondportion of the modulated optical signal from the second opticalcommunication path and supply the second portion of the modulatedoptical signal to the second input of the optical combiner.

In some implementations, the apparatus can include a wavelengthselective switch operable to be coupled to a first optical communicationpath including a first optical fiber and a second optical communicationpath including a second optical fiber. The wavelength selective switchcan be operable to receive the first portion of the modulated opticalsignal from the first optical communication path and supply the firstportion of the modulated optical signal to the first input of theoptical combiner. The wavelength selective switch can be operable toreceive the second portion of the modulated optical signal from thesecond optical communication path and supply the second portion of themodulated optical signal to the second input of the optical combiner.

In some implementations, that apparatus can include a local oscillatorlaser that supplies light. At least a portion of the light can besupplied to the optical hybrid circuitry.

In some implementations, the apparatus can include an optical splitterthat receives the light from the local oscillator laser and supplies tothe portion of the light to the optical hybrid circuitry.

In another aspect, an apparatus includes a first digital signalprocessor that is operable to receive information signals including afirst plurality of bits of information and provide a first plurality ofdigital signals based on the information signals; digital-to-analogconversion circuitry operable to receive the first plurality of digitalsignals from the first digital signal processor and provide a pluralityof analog signals based on the digital signals; driver circuitryoperable to output drive signals based on the analog signals; an opticalmodulator operable to modulate an optical signal based on the drivesignals to provide a first modulated optical signal, the first modulatedoptical signal including a first group of optical subcarriers and asecond group of optical subcarriers, the first group of opticalsubcarriers including a first optical subcarrier and the second group ofoptical subcarriers including a second optical subcarrier, the firstoptical subcarrier carrying first data and the second optical subcarriercarrying second data, the first and second data being indicative of thefirst plurality of bits of information; a polarization beam splitterthat is operable to receive a second modulated optical signal, thesecond modulated optical signal including a third group of opticalsubcarriers and a fourth group of optical subcarriers, the third groupof optical subcarriers including a third optical subcarrier and thefourth group of optical subcarriers including a fourth opticalsubcarrier, the third optical subcarrier carrying third data and thefourth optical subcarrier carrying fourth data, the third data beingindicative of a second plurality of bits of information and the seconddata being indicative of the second plurality of bits of information;optical hybrid circuitry operable to receive outputs from thepolarization beam splitter and supply a plurality of optical mixingproducts; photodetector circuitry operable to supply electrical signalsbased on the plurality of optical mixing products; analog-to-digitalconversion circuitry operable to provide a second plurality of digitalsignals based on the electrical signals; and a digital signal processoroperable to output the second plurality of bits based on the secondplurality of digital signals.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, each subcarrier of the first group of opticalsubcarriers can have a corresponding one of a first plurality offrequencies and each subcarrier of the third group of opticalsubcarriers can have a corresponding one of the first plurality offrequencies.

In some implementations, each subcarrier of the second group of opticalsubcarriers can have a corresponding one of a second plurality offrequencies and each subcarrier of the fourth group of opticalsubcarriers can have a corresponding one of the second plurality offrequencies.

In some implementations, each optical subcarrier of the first group ofoptical subcarriers, each optical subcarrier of the second group ofoptical subcarriers, each optical subcarriers of the third group ofoptical subcarriers, and each optical subcarrier of the fourth group ofoptical subcarriers can be a Nyquist subcarrier.

In some implementations, the first data can be the same as the seconddata and the third data can be the same as the fourth data.

In some implementations, a guard band can spectrally separate firstfrequencies associated with the first group of optical subcarriers fromsecond frequencies associated with the second group of opticalsubcarriers.

In some implementations, the apparatus can include an optical splitterhaving an input that receives the first modulated optical signal, afirst output that supplies a first portion of the first modulatedoptical signal and a second output that supplies a second portion of thefirst modulated optical signal.

In some implementations, the apparatus can include an optical combinerhaving a first input that receives a first portion of the secondmodulated optical signal including the third group of opticalsubcarriers and a second portion of the second modulated opticalincluding the fourth group of the optical subcarriers.

In some implementations, the apparatus can include a first wavelengthselective switch that receives the first portion of the first modulatedoptical signal and supplies the first group of optical subcarriers to afirst optical communication path including a first optical fiber; and asecond wavelength selective switch that receives the second portion ofthe first modulated optical signal and supplies the second group ofoptical subcarriers to a second optical communication path including asecond optical fiber.

In some implementations, the apparatus can include a third wavelengthselective switch operable to be coupled to the second opticalcommunication path including the second optical fiber. The thirdwavelength selective switch can be operable to receive the first portionof the second modulated optical signal including the third group ofoptical subcarriers from the second optical communication path andsupply the first portion of the second modulated optical signal to thefirst input of the optical combiner. The apparatus can also include afourth wavelength selective switch operable to be coupled to the firstoptical communication path including the first optical fiber. The fourthwavelength selective switch can be operable to receive the secondportion of the second modulated optical signal including the fourthgroup of subcarriers from the first optical communication path andsupply the second portion of the second modulated optical signal to thesecond input of the optical combiner.

In some implementations, the apparatus can include a first wavelengthselective switch operable to receive the first portion of the firstmodulated optical signal and the second portion of the first modulatedoptical signal. The first wavelength selective switch can supply thefirst group of optical subcarriers to a first optical communication pathincluding a first optical fiber. The first wavelength selective switchcan supply the second group of optical subcarriers to a second opticalcommunication path including a second optical fiber. The apparatus canalso include a second wavelength selective switch operable to be coupledto the second optical communication path including the second opticalfiber and can be operable to receive the first portion of the secondmodulated optical signal from the second optical communication path andsupply the first portion of the second modulated optical signalincluding the third group of optical subcarriers to the first input ofthe optical combiner. The second wavelength selective switch can beoperable to be coupled to the first optical communication path includingthe first optical fiber. The second wavelength selective switch can beoperable to receive the second portion of the second modulated opticalsignal including the fourth plurality of optical subcarriers from thefirst optical communication path and supply the second portion of thesecond modulated optical signal to the second input of the opticalcombiner.

In another aspect, an apparatus includes a digital signal processor thatis operable to receive a plurality of bits of information and provide aplurality of digital signals based on the plurality of bits ofinformation; digital-to-analog conversion circuitry operable to receivethe digital signals from the digital signal processor and provide aplurality of analog signals based on the digital signals; drivercircuitry operable to output drive signals based on the analog signals;a laser operable to provide an optical signal; and an optical modulatoroperable to modulate at least a portion of the optical signal based onthe drive signals to provide a modulated optical signal. The modulatedoptical signal includes a first optical subcarriers and a second opticalsubcarrier. The first optical subcarrier carries first data and thesecond optical subcarrier carries second data. The first and second dataare indicative of the plurality of bits of information.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, the first data can be the same as the seconddata.

In some implementations, the apparatus can include an optical splitter.The splitter can have an input and first and second outputs. The inputcan be operable to receive the modulated optical signal. The firstoutput can be operable to supply a first portion of the modulatedoptical signal. The second output can be operable to supply a secondportion of modulated optical signal.

In some implementations, the first portion of the modulated opticalsignal can be a first power-split portion of the modulated opticalsignal and the second portion of the modulated optical signal can be asecond power-split portion of the modulated optical signal.

In some implementations, the apparatus can include a wavelengthselective switch that receives the first portion of the modulatedoptical signal.

In some implementations, the apparatus can include a first wavelengthselective switch that receives the first portion of the modulatedoptical signal; and a second wavelength selective switch that receivesthe second portion of the modulated optical signal.

In some implementations, the first wavelength selective switch cansupply the first optical subcarrier to a first optical communicationpath including a first optical fiber and the second wavelength selectiveswitch can supply the second optical subcarrier to a second opticalcommunication path including a second optical fiber.

In some implementations, each of the first and second opticalsubcarriers can be a Nyquist subcarrier.

In some implementations, the apparatus can include a wavelengthselective switch that receives the first portion of the modulatedoptical signal and the second portion of the modulated optical signal.

In some implementations, the wavelength selective switch can supply thefirst optical subcarrier to a first optical communication path includinga first optical fiber, and the wavelength selective switch can supplythe second group of optical subcarriers to a second opticalcommunication path including a second optical fiber.

In some implementations, the apparatus can include an optical splitter.The optical splitter can receive the optical signal from the laser andsupply said at least a portion of the optical signal to the modulator.

In another aspect, an apparatus includes a polarization beam splitterthat is operable to receive a first modulated optical signal and asecond modulated optical signal. The first modulated optical signalincludes a first group of optical subcarriers and the second modulatedoptical signal includes a second group of optical subcarriers. The firstgroup of optical subcarriers includes a first optical subcarrier. Thesecond group of optical subcarriers includes a second opticalsubcarrier. The first optical subcarrier carries first data and thesecond optical subcarrier carrying second data. The first data isindicative of a plurality of bits of information. The second data isindicative of the plurality of bits of information. The apparatus alsoincludes optical hybrid circuitry operable to receive outputs from thepolarization beam splitter and supply a plurality of optical mixingproducts; photodetector circuitry operable to supply electrical signalsbased on the plurality of optical mixing products; analog-to-digitalconversion circuitry operable to provide digital signals based on theelectrical signals; and a digital signal processor operable to outputthe plurality of bits based on the digital signals.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, the first data can be the same as the seconddata.

In some implementations, a guard band can spectrally separate firstfrequencies associated with the first group of optical subcarriers fromsecond frequencies associated with the second group of opticalsubcarriers.

In some implementations, the apparatus can include an optical combinerhaving a first input that receives the first modulated optical signaland a second input that receives the second modulated optical signal.The optical combiner can have an output that supplies the first and thesecond modulated optical signals.

In some implementations, the apparatus can include a first wavelengthselective switch operable to be coupled to a first optical communicationpath including a first optical fiber. The first wavelength selectiveswitch can be operable to receive the first modulated optical signalfrom the first optical communication path and supply the first modulatedoptical signal to the first input of the optical combiner. The apparatuscan also include a second wavelength selective switch operable to becoupled to a second optical communication path including a secondoptical fiber. The second wavelength selective switch can be operable toreceive the second modulated optical signal from the second opticalcommunication path and supply the second modulated optical signal to thesecond input of the optical combiner.

In some implementations, the apparatus can include a wavelengthselective switch operable to be coupled to a first optical communicationpath including a first optical fiber and a second optical communicationpath including a second optical fiber. The wavelength selective switchcan be operable to receive the first modulated optical signal from thefirst optical communication path and supply the first modulated opticalsignal to the first input of the optical combiner. The wavelengthselective switch can be operable to receive the second modulated opticalsignal from the second optical communication path and supply the secondmodulated optical signal to the second input of the optical combiner.

In some implementations, the apparatus can include a local oscillatorlaser that supplies light, at least a portion of the light beingsupplied to the optical hybrid circuitry.

In some implementations, the apparatus can include an optical splitterthat receives the light from the local oscillator laser and supplies tothe portion of the light to the optical hybrid circuitry.

In another aspect, an apparatus includes a first digital signalprocessor that is operable to receive a first plurality of bits ofinformation and provide a first plurality of digital signals based onthe first plurality of bits of information; digital-to-analog conversioncircuitry operable to receive the first plurality of digital signalsfrom the first digital signal processor and provide a plurality ofanalog signals based on the digital signals; driver circuitry operableto output drive signals based on the analog signals; an opticalmodulator operable to modulate an optical signal based on the drivesignals to provide a first modulated optical signal, the first modulatedoptical signal including a first optical subcarrier and a second opticalsubcarrier, the first optical subcarrier carrying first data and thesecond optical subcarrier carrying second data, the first and seconddata being indicative of the first plurality of bits of information; apolarization beam splitter that is operable to receive a secondmodulated optical signal, the second modulated optical signal includinga first group of optical subcarriers and a second group of opticalsubcarriers, the first group of optical subcarriers including a thirdoptical subcarrier and the second group of optical subcarriers includinga fourth optical subcarrier, the third optical subcarrier carrying thirddata and the fourth optical subcarrier carrying fourth data, the thirddata being indicative of a second plurality of bits of information andthe second data being indicative of the second plurality of bits ofinformation; optical hybrid circuitry operable to receive outputs fromthe polarization beam splitter and supply a plurality of optical mixingproducts; photodetector circuitry operable to supply electrical signalsbased on the plurality of optical mixing products; analog-to-digitalconversion circuitry operable to provide a second plurality of digitalsignals based on the electrical signals; and a second digital signalprocessor operable to output the second plurality of bits based on thesecond plurality of digital signals.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, each subcarrier of the first group of opticalsubcarriers can have a corresponding one of a first plurality offrequencies and each subcarrier of the second group of opticalsubcarriers can have a corresponding one of a second plurality offrequencies. The first optical subcarrier can have one of the firstplurality of frequencies, and the second optical subcarrier can havesaid one of the first plurality of frequencies.

In some implementations, each of the first and second opticalsubcarriers can be a Nyquist subcarrier.

In some implementations, the first data can be the same as the seconddata and the third data is the same as the fourth data.

In some implementations, a guard band can spectrally separate firstfrequencies associated with the first group of optical subcarriers fromsecond frequencies associated with the second group of opticalsubcarriers.

In some implementations, the apparatus can include an optical splitterhaving an input that receives the first modulated optical signal, afirst output that supplies a first portion of the first modulatedoptical signal and a second output that supplies a second portion of thefirst modulated optical signal.

In some implementations, the apparatus can include an optical combinerhaving a first input that receives a first portion of the secondmodulated optical signal including the first group of opticalsubcarriers and a second portion of the second modulated opticalincluding the second group of optical subcarriers.

In some implementations, the apparatus can include a first wavelengthselective switch that is operable to receive the first portion of thefirst modulated optical signal and supply the first optical subcarrierto a first optical communication path including a first optical fiber;and a second wavelength selective switch that receives the secondportion of the first modulated optical signal and supplies the secondoptical subcarrier to a second optical communication path including asecond optical fiber.

In some implementations, the apparatus can include a third wavelengthselective switch operable to be coupled to the second opticalcommunication path including the second optical fiber. The thirdwavelength selective switch can be operable to receive the first portionof the second modulated optical signal including the first group ofoptical subcarriers from the second optical communication path andsupply the first portion of the second modulated optical signal to thefirst input of the optical combiner. The apparatus can also include afourth wavelength selective switch operable to be coupled to the firstoptical communication path including the first optical fiber. The fourthwavelength selective switch can be operable to receive the secondportion of the second modulated optical signal including the fourthoptical subcarrier from the first optical communication path and supplythe second portion of the second modulated optical signal to the secondinput of the optical combiner.

In some implementations, the apparatus can include a first wavelengthselective switch operable to receive the first portion of the firstmodulated optical signal and the second portion of the first modulatedoptical signal. The first wavelength selective switch can supply thefirst optical subcarrier to a first optical communication path includinga first optical fiber. The first wavelength selective switch can supplythe second optical subcarrier to a second optical communication pathincluding a second optical fiber. The apparatus can also include asecond wavelength selective switch operable to be coupled to the secondoptical communication path including the second optical fiber andoperable to receive the first portion of the second modulated opticalsignal from the second optical communication path and supply the firstportion of the second modulated optical signal including the first groupof optical subcarriers to the first input of the optical combiner. Thesecond wavelength selective switch can be operable to be coupled to thefirst optical communication path including the first optical fiber. Thesecond wavelength selective switch can be operable to receive the secondportion of the second modulated optical signal including the secondgroup of optical subcarriers from the first optical communication pathand supply the second portion of the second modulated optical signal tothe second input of the optical combiner.

As another aspect, an apparatus includes a digital signal processor thatis operable to receive a plurality of bits of information and provide aplurality of digital signals based on the plurality of bits ofinformation; digital-to-analog conversion circuitry operable to receivethe digital signals from the digital signal processor and provide aplurality of analog signals based on the digital signals; drivercircuitry operable to output drive signals based on the analog signals;a laser operable to provide an optical signal; an optical modulatoroperable to modulate at least a portion of the optical signal based onthe drive signals to provide a modulated optical signal, the modulatedoptical signal including a an optical subcarrier, the optical subcarriercarrying data indicative of the plurality of bits of information; and anoptical splitter operable to receive the modulated optical signal, theoptical splitter having first and second outputs, the first outputsupplying a first portion of modulated optical signal and the secondoutput supplying a second portion of the modulated optical signal.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, the first portion of the modulated opticalsignal can be supplied to a first optical communication path including afirst optical fiber and the second portion of the modulated opticalsignal can be supplied to a second optical communication path includinga second optical fiber.

In some implementations, the first portion of the modulated opticalsignal can be a first power-split portion of the modulated opticalsignal and the second portion of the modulated optical signal can be asecond power-split portion of the modulated optical signal.

In some implementations, the apparatus can further include a wavelengthselective switch that receives the first portion of the modulatedoptical signal and supplies the first portion of the modulated opticalsignal to an optical communication path including an optical fiber.

In some implementations, the apparatus can further include a firstwavelength selective switch that receives the first portion of themodulated optical signal and provides the first portion of the modulatedoptical signal to a first optical communication path including a firstoptical fiber; and a second wavelength selective switch that receivesthe second portion of the modulated optical signal and provides thesecond portion of the modulated optical signal to a second opticalcommunication path including a second optical fiber.

In some implementations, the optical subcarrier can be a Nyquistsubcarrier.

In some implementations, the apparatus can further include a wavelengthselective switch that receives the first portion of the modulatedoptical signal and the second portion of the modulated optical signal.

In some implementations, the wavelength selective switch can supply thefirst portion of the modulated optical signal to a first opticalcommunication path including a first optical fiber, and the wavelengthselective switch can supply the second portion of the modulated opticalsignal to a second optical communication path including a second opticalfiber.

In some implementations, the optical splitter can be a first opticalsplitter, and the apparatus can further include a second opticalsplitter operable to receive the optical signal from the laser andsupply said at least a portion of the optical signal to the modulator.

In another aspect, an apparatus includes a first digital signalprocessor that is operable to receive a first plurality of bits ofinformation and provide a first plurality of digital signals based onthe first plurality of bits of information; digital-to-analog conversioncircuitry operable to receive the first plurality of digital signalsfrom the first digital signal processor and provide a plurality ofanalog signals based on the digital signals; driver circuitry operableto output drive signals based on the analog signals; an opticalmodulator operable to modulate an optical signal based on the drivesignals to provide a first modulated optical signal, the first modulatedoptical signal including a first optical subcarrier, the first opticalsubcarrier carrying data indicative of the first plurality of bits ofinformation; a splitter operable to receive the first modulated opticalsignal, the splitter having first and second outputs, the first outputbeing operable to provide a first portion of the first modulated opticalsignal and the second output being operable to provide a second portionof the first modulated optical signal; a polarization beam splitter thatis operable to receive a second modulated optical signal and a thirdmodulated optical signal, the second modulated optical signal includinga group of second optical subcarriers and a group of third opticalsubcarriers, the group of second optical subcarriers including a secondoptical subcarrier and the group of third optical subcarriers includinga third optical subcarrier, the second optical subcarrier carryingsecond data and the third optical subcarrier carrying third data, thesecond data being indicative of a second plurality of bits ofinformation and the third data being indicative of the second pluralityof bits of information; optical hybrid circuitry operable to receiveoutputs from the polarization beam splitter and supply a plurality ofoptical mixing products; photodetector circuitry operable to supplyelectrical signals based on the plurality of optical mixing products;analog-to-digital conversion circuitry operable to provide a secondplurality of digital signals based on the electrical signals; and asecond digital signal processor operable to output the second pluralityof bits based on the second plurality of digital signals.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, each subcarrier of the group of second opticalsubcarriers can have a corresponding one of a first plurality offrequencies and each subcarrier of the group of third opticalsubcarriers can have a corresponding one of a second plurality offrequencies. The first optical subcarrier can have one of the firstplurality of frequencies, and the second optical subcarrier can havesaid one of the second plurality of frequencies.

In some implementations, each of the first optical subcarrier, the groupof second optical subcarriers, and the group of third opticalsubcarriers can be a Nyquist subcarrier.

In some implementations, the second data can be the same as the thirddata.

In some implementations, a guard band can spectrally separate firstfrequencies associated with the first optical subcarrier from secondfrequencies associated with the second group of optical subcarriers.

In some implementations, the apparatus can further include an opticalcombiner having a first input that receives the group of second opticalsubcarriers and the group of third optical subcarriers.

In some implementations, the apparatus can further include a firstwavelength selective switch operable to receive the first portion of thefirst modulated optical signal and supply the first portion of the firstmodulated optical signal to a first optical communication path includinga first optical fiber; and a second wavelength selective switch thatreceives the second portion of the first modulated optical signal andsupplies the second portion of the first modulated optical signal to asecond optical communication path including a second optical fiber.

In some implementations, the apparatus can further include a thirdwavelength selective switch operable to be coupled to the second opticalcommunication path including the second optical fiber, the thirdwavelength selective switch being operable to receive the secondmodulated optical signal including the group of second opticalsubcarriers from the second optical communication path and supply thesecond modulated optical signal to the first input of the opticalcombiner; and a fourth wavelength selective switch operable to becoupled to the first optical communication path including the firstoptical fiber, the fourth wavelength selective switch being operable toreceive the third modulated optical signal including the group of thirdoptical subcarriers from the first optical communication path and supplythe third modulated optical signal to the second input of the opticalcombiner.

In some implementations, the apparatus can further include an opticalcombiner having a first and second inputs and an output; a firstwavelength selective switch operable to receive the first portion of thefirst modulated optical signal and the second modulated optical signal,where the first wavelength selective switch supplies the first portionof the modulated optical signal to a first optical communication pathincluding a first optical fiber, and the first wavelength selectiveswitch supplies the second modulated optical signal to the first inputof the optical combiner; and a second wavelength selective switchoperable to receive the second portion of the second modulated opticalsignal and the third modulated optical signal, where the secondwavelength selective switch supplies the second portion of the firstmodulated optical to a second optical communication path including asecond optical fiber, and the second wavelength selective switchsupplies the third modulated optical signal to the second input of theoptical combiner, the output of the optical combiner providing thesecond and third modulated optical signals to the polarization beamsplitter.

In some implementations, the apparatus can further include an opticalcombiner having a first input that receives the second modulated opticalsignal, a second input that receives the second modulated opticalsignal, and an output that provides the second and third modulatedoptical signals to the polarization beam splitter.

In another aspect, an apparatus includes a first transmitter and asecond transmitter. The first transmitter includes a first laseroperable to provide a first optical signal, and a first modulatoroperable to provide a first modulated optical signal based on the firstoptical signal and a plurality of data stream provided to the firsttransmitter, the first modulated optical signal including a firstplurality of optical subcarriers, such that the first transmitter isoperable to supply the first modulated optical signal to a first opticalcommunication path, the first plurality of optical subcarriers beingassociated with the plurality of data streams. The second transmitter isoperable to receive the plurality of data streams. The secondtransmitter includes a second laser operable to provide a second opticalsignal; and a second modulator operable to provide a second modulatedoptical signal based on the second optical signal and the plurality ofdata streams, the second modulated optical signal including a secondplurality of optical subcarriers, such that the second transmitter isoperable to supply the second modulated optical signal to a secondoptical communication path, the second plurality of optical subcarriersbeing associated with the plurality of data streams.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, each optical subcarrier of the first pluralityof optical subcarriers and each optical subcarrier of the secondplurality of optical subcarriers can be a Nyquist subcarrier.

In some implementations, the apparatus can further include a firstwavelength selective switch operable to receive the first plurality ofoptical subcarriers from the first transmitter and supply the firstplurality of optical subcarriers to the first optical communicationpath; and a second wavelength selective switch operable to receive thesecond plurality of optical subcarriers and supply the second pluralityof optical subcarriers to the second optical communication path.

In some implementations, the optical signal provided by the first lasercan have a first wavelength and the optical signal provided by thesecond laser can have a second wavelength different than the firstwavelength.

In some implementations, each of the first plurality of opticalsubcarriers can have a corresponding one of a first plurality offrequencies, and each of the second plurality of optical subcarriers canhave a corresponding one of a second plurality of frequencies.

In some implementations, each of the first plurality of frequencies canbe different than each of the second plurality of frequencies.

In some implementations, the first transmitter further can include afirst digital signal processor operable to provide first digital signalsbased on the first plurality of data streams, first digital-to-analogcircuitry operable to provide first analog signals based on the firstdigital signals, and first driver circuitry operable to provide firstdrive signals to the first modulator based on the first analog signals.The second transmitter can include a second digital signal processoroperable to provide second digital signals based on the first pluralityof data streams, second digital-to-analog circuitry operable to providesecond analog signals based on the second digital signals, and seconddriver circuitry operable to provide second drive signals to the secondmodulator based on the second analog signals.

In another aspect, an apparatus includes a first receiver, a secondreceiver, and a selection circuit. The first receiver includes a firstpolarization beam splitter operable to receive a first modulated opticalsignal from a first optical communication path, the first modulatedoptical signal including a first plurality of optical subcarriersassociated with a plurality of data streams, and a first digital signalprocessor operable to provide an output based on the first plurality ofoptical subcarriers, the output of the first digital signal processorincluding the plurality of data streams. The second receiver includes asecond polarization beam splitter operable to receive a second modulatedoptical signal from a second optical communication path, the secondmodulated optical signal including a second plurality of opticalsubcarriers, each of which being associated with the plurality of datastreams, a second digital signal processor operable to provide an outputbased on the second plurality of optical subcarriers, the output of thesecond digital processor including the plurality of data streams. Theselection circuit is coupled to the first digital signal processor andthe second digital processor. The selection circuit is configured toselectively supply one of the output of the first digital signalprocessor and the output of the second digital processor.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, each optical subcarrier of the first pluralityof optical subcarriers and each optical subcarrier of the secondplurality of optical subcarriers can be a Nyquist subcarrier.

In some implementations, the apparatus can further include a firstwavelength selective switch operable to the supply the first pluralityof optical subcarriers to the first receiver; and a second wavelengthselective switch operable to supply the second plurality of opticalsubcarriers to the second receiver.

In some implementations, the apparatus can further include a first laseroperable to provide a first local oscillator signal; a first opticalhybrid circuit operable to receive the first local oscillator signal andoutputs from the first polarization beam splitter; a second laseroperable to provide a second local oscillator signal; and a secondoptical hybrid circuit operable to receive the second local oscillatorsignal the outputs from the second polarization beam splitter.

In some implementations, the first local oscillator signal can have afirst wavelength and the second local oscillator signal can have asecond wavelength different than the first wavelength.

In some implementations, each of the first plurality of opticalsubcarriers can have a corresponding one of a first plurality offrequencies, and each of the second plurality of optical subcarriers canhave a corresponding one of a second plurality of frequencies.

In some implementations, each of the first plurality of frequencies canbe different than each of the second plurality of frequencies.

In another aspect, an apparatus includes a first transmitter, a secondtransmitter, a first receiver, a second receiver, and a selectioncircuit. The first transmitter includes a first laser operable toprovide a first optical signal, and a first modulator operable toprovide a first modulated optical signal based on the first opticalsignal and a first plurality of data stream provided to the firsttransmitter, the first modulated optical signal including a firstplurality of optical subcarriers, such that the first transmitter isoperable to supply the first modulated optical signal to a first opticalcommunication path, the first plurality of optical subcarriers beingassociated with the first plurality of data stream. The secondtransmitter is operable to receive the plurality of data streams. Thesecond transmitter includes a second laser operable to provide a secondoptical signal; a second modulator operable to provide a secondmodulated optical signal based on the second optical signal and thefirst plurality of data streams, the second modulated optical signalincluding a second plurality of optical subcarriers, such that thesecond transmitter is operable to supply the second modulated opticalsignal to a second optical communication path, the second plurality ofoptical subcarriers being associated with the first plurality of datastreams. The first receiver includes a first polarization beam splitteroperable to receive a third modulated optical signal from the secondoptical communication path, the third modulated optical signal includinga third plurality of optical subcarriers associated with a secondplurality of data streams, and a first digital signal processor operableto provide an output based on the third plurality of opticalsubcarriers, the output of the first digital signal processor includingthe second plurality of data streams. The second receiver includes asecond polarization beam splitter operable to receive a fourth modulatedoptical signal from the first optical communication path, the fourthmodulated optical signal including a fourth plurality of opticalsubcarriers, each of which being associated with the second plurality ofdata streams, and a second digital signal processor operable to providean output based on the second plurality of optical subcarriers, theoutput of the second digital processor including the second plurality ofdata streams. The selection circuit is coupled to the first digitalsignal processor and the second digital processor. The selection circuitis configured to selectively supply one of the output of the firstdigital signal processor and the output of the second digital processor.

In some implementations, the apparatus can include a first wavelengthselective switch coupled to the first and second optical communicationpaths, the first wavelength selective switch being operable to receivethe first plurality of optical subcarrier from the first transmitter andsupply the first plurality of optical subcarriers to the first opticalcommunication path, and the first wavelength selective switch beingoperable to receive the third plurality of optical subcarriers from thesecond optical communication path and provide the third plurality ofoptical subcarriers to the first receiver; and a second wavelengthselective switch coupled to the first and second optical communicationpaths, the second wavelength selective switch being operable to receivethe second plurality of optical subcarrier from the second transmitterand supply the second plurality of optical subcarriers to the secondoptical communication path, and the second wavelength selective switchbeing operable to receive the fourth plurality of optical subcarriersfrom the first optical communication path and provide the fourthplurality of optical subcarriers to the second receiver.

In some implementations, each optical subcarrier of the first pluralityof optical subcarriers and each optical subcarrier of the secondplurality of optical subcarriers can be a Nyquist subcarrier.

In some implementations, the optical signal provided by the first lasercan have a first wavelength and the optical signal provided by thesecond laser can have a second wavelength different than the firstwavelength.

In some implementations, each of the first plurality of opticalsubcarriers can have a corresponding one of a first plurality offrequencies, and each of the second plurality of optical subcarriers canhave a corresponding one of a second plurality of frequencies.

In some implementations, each of the first plurality of frequencies canbe different than each of the second plurality of frequencies.

In some implementations, each of the third plurality of opticalsubcarriers can have a corresponding one of the first plurality offrequencies, and each of the fourth plurality of optical subcarriers canhave a corresponding one of the second plurality of frequencies.

Other implementations are directed to systems, devices, andnon-transitory, computer-readable media having instructions storedthereon, that when executed by one or more processors, cause the one ormore processors to perform operations described herein.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram of an example optical communications network.

FIG. 1B is a diagram of another example optical communications network.

FIGS. 2A-2B are diagrams of an example process for transmitting databetween nodes of an optical communications network.

FIG. 3 is a diagram of example optical subcarriers according to afrequency domain.

FIGS. 4A and 4B are diagrams of example hub nodes.

FIG. 5 is a diagram of an example leaf node.

FIG. 6 is a diagram of an example severing of an optical path in anoptical communications network.

FIGS. 7A-7C are diagrams of example processes for receiving data using aleaf node.

FIG. 8 is a diagram of another example process for transmitting databetween nodes of an optical communications network.

FIG. 9 is a diagram of example hub nodes.

FIG. 10 is a diagram of an example transmitter than can be included in anetwork node.

FIG. 11A is a diagram of an example digital signal processor (DSP).

FIG. 11B is a diagram of example frequency bins.

FIG. 11C is a diagram of example pulse shape filters.

FIG. 12 is a diagram of an example optical receiver.

FIG. 13 is a diagram of an example receiver DSP.

FIG. 14 is a diagram of an example leaf node transmitter

FIG. 15 is a diagram of an example hub node receiver.

FIGS. 16A-16D are flow chart diagrams of example processes that can beperformed using one or more of the systems described herein.

FIG. 17 is a diagram of an example computer system.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

The present disclosure describes systems and methods for mitigating theeffects of severed and/or malfunctioned optical links in an opticalcommunications system.

In some implementations, a first network node (e.g., a first computerdevice) can transmit multiple instances of a particular portion of datato a second network node (e.g., a second computer device) concurrentlyusing multiple different optical paths, each of the optical paths havingone or more respective optical links. For example, the first networknode can generate a first optical signal, modulate the first opticalsignal based on the data (e.g., using a first optical subcarrier), andtransmit the optical signal to the second network node over a firstoptical path. Further, the first network node can generate a secondoptical signal based on the data (e.g., using a second opticalsubcarrier), and transmit the optical signal to the second network nodeover a second optical path different from the first optical path.

During normal operation (e.g., when both the first optical path and thesecond optical path are intact and do not have any malfunctioningoptical links or equipment), the second network node can recover thedata from the optical signal received from one of the optical links(e.g., by demodulating the optical signal received over that opticalpath). In some implementations, such an optical path may be referred toas a “working” path.

If one of the optical paths include severed or malfunctioning opticallinks or equipment, the second network node still can recover the datafrom the optical signals received from the other optical link (e.g., bydemodulating the optical signal received over the other optical path).In some implementations, this other optical path may be referred to as a“protection” path. Accordingly, the connectivity between the firstnetwork node and the second network node can be maintained, despitesevered or inoperable optical links.

In some implementations, one of the optical paths (e.g., a “working”path) may include malfunctioning optical links or equipment that enableoptical signals to be conveyed between network nodes, but in a degradedform. For example, the optical signals exhibit a particular degree ofattenuation, contain a particular amount of noise or other interference,or exhibit other characteristics that may make it more difficult torecover the data. In this situation, a network node can receive a secondoptical signal from another optical path (e.g., a “protection” path),compare the characteristics of the optical signals received from eachoptical path, and select one of the optical signals for furtherprocessing (e.g., based on an estimated quality of each of the opticalsignals). Accordingly, the connectivity between the first network nodeand the second network node can be maintained, despite malfunctioningoptical links or equipment.

In some implementations, “working” paths and “protection” paths can beimplemented as an access ring. For example, an access ring can include afirst unidirectional optical path that communicatively couples multiplenetwork nodes in a first sequence, and a second unidirectional opticalpath that communicatively couples the same network nodes in a secondsequence, where the first sequence is the reverse of the secondsequence. As a simplified example, if each of the network nodes arearranged in a circle, the first optical path can communicatively couplethe network nodes by conveying optical signals to each of the networknodes in a sequence in a clockwise direction, and the second opticalpath can communicatively couple the network nodes by conveying opticalsignals to each of the same network nodes in a sequence in acounterclockwise direction. One of the optical paths can be implementedas a “working” path for at least some of the network nodes, and theother one of the optical paths can be implemented as a “protection” pathfor at least some of the network nodes.

In some implementations, at least some of the subcarriers described canbe Nyquist subcarriers. A Nyquist subcarrier is a group of opticalsignals, each carrying data, where (i) the spectrum of each such opticalsignal within the group is sufficiently non-overlapping such that theoptical signals remain distinguishable from each other in the frequencydomain, and (ii) such group of optical signals is generated bymodulation of light from a single laser. In general, each subcarrier mayhave an optical spectral bandwidth that is at least equal to the Nyquistfrequency, as determined by the baud rate of such subcarrier.

Example systems and techniques for mitigating the effects of severedand/or malfunctioned optical links in an optical communications systemare described in greater detail below and shown in the drawings.

I. Example System and Methods for Mitigating the Effects of Severedand/or Malfunctioned Optical Links in an Optical Communications System

FIG. 1A shows an example optical communications network 100. The opticalcommunications network 100 includes multiple network nodes that arecommunicatively coupled to one another by an access ring 102.

In this example, the network nodes include a hub node 104 (“Hub”) and Nleaf nodes 106 a-106 n (“Leaf-1,” “Leaf-2,” . . . “Leaf-n”). Each of thenetwork nodes can include one or more respective computer devices (e.g.,server computers, client computers, etc.). In some implementations, thenetwork nodes can be configured such that the hub node 104 transmitsand/or receives data from each of the leaf nodes 106 a-106 n. Forexample, the hub node 104 can receive data (e.g., from another networknode) that is intended for one of the leaf nodes 106 a-106 n, and routethe data to that leaf node 106 a-106 n. As another example, a leaf node106 a-106 n can generate data that is intended for another networkdevice, and route the data to the hub node 104 for delivery to theintended network device. Although a single hub node 104, this is merelyan illustrative example. In practice, an optical communications networkcan include any number of hub nodes. Similarly, an opticalcommunications network can include any number of leaf nodes.

As shown in FIG. 1A, the network nodes are communicatively coupled toone another using an access ring 102. In this example, the access ring102 includes two optical paths 108 a and 108 b (which may also bereferred to as optical communication paths). The first optical path 108a communicatively couples the hub node 104 and the leaf nodes 106 a-106n in a sequence in a first direction (e.g., a clockwise direction). Thesecond optical path 108 b communicatively couples the hub node 104 andthe leaf nodes 106 a-106 n in a sequence in a second direction (e.g., acounterclockwise direction). Each of the optical paths 108 a and 108 bcan be implemented using one or more optical links (e.g., optical fiber)and/or equipment interconnecting the optical links (e.g., line systemcomponents).

As described above, the optical communications network 100 can beconfigured to mitigate the effects of severed and/or malfunctionedoptical links in the access ring 102.

For example, referring to FIG. 2A, the hub node 104 can be configured totransmit multiple instances of a particular portion of data to one ofthe more of the leaf nodes 106 a-106 n concurrently using the opticalpaths 108 a and 108 b. For instance, the hub node 104 can receive dataintended for each of the leaf nodes 106 a-106 n (e.g., eight portions ofdata D1-D8 intended for eight leaf nodes 106 a-106 h, respectively). Thehub node 104 can generate a first optical signal, modulate the firstoptical signal based on the data D1-D8 (e.g., using respective opticalsubcarriers assigned to or allotted to the leaf nodes 106 a-106 h), andtransmit the first optical signal over the first optical path 108 a.With reference to this data transmission, the first optical path 108 amay be referred to as the “hub working Tx” path or the “leaf working Rx”path.

Further, the hub node 104 can generate a second optical signal, modulatethe second optical signal based on the data D1-D8 (e.g., usingrespective optical subcarriers assigned to or allotted to the leaf nodes106 a-106 h), and transmit the second optical signal over the secondoptical path 108 b, concurrently with the transmission of the firstoptical signal over the optical path 108 a. With reference to this datatransmission, the second optical path 108 b may be referred to as the“hub protect Tx” path or the “leaf protect Rx” path.

In some implementations, the information transmitted by the hub node 104along the first optical path 108 a can be identical to the informationtransmitted by the hub node 104 along the second optical path 108 b.

In some implementations, the information transmitted by the hub node 104along the first optical path 108 a can be different from the informationtransmitted by the hub node 104 along the second optical path 108 b. Forexample, the first information and the second information can includethe same data modulated according to different digital subcarriers(e.g., as described above). As another example, the first informationand the second information can include the same data transmittedaccording to different forward error correction (FEC) schemes (e.g., byincluding different FEC codes or bits). For instance, as shown in FIG.2A, the length of the first optical path 108 a from the hub node 104 tothe leaf node 106 b (e.g., 60 km) can be different from the length ofthe second optical path 108 b from the hub node 104 and to leaf node 106b (40 km). Due to this difference, the hub node 104 can transmit dataintended to the second leaf 106 b according to different FEC schemes(e.g., by including different FEC codes or bits), depending on theoptical path this is used.

During normal operation (e.g., when both the first optical path 108 aand the second optical path 108 b are intact and do not have anymalfunctioning optical links or equipment), each of the leaf nodes 106a-106 h can recover the respective data D1-D8 from the optical signalreceived from the first optical path 108 a (e.g., by demodulating theoptical signal received over that optical path, in particular theoptical subcarrier that was assigned to or allotted to that leaf node).For example, referring to FIG. 2A, the leaf node 106 a can recover thedata D1, the leaf node 106 b can recover the data D2, and so forth.

However, if the first optical path 108 a includes severed ormalfunctioning optical links or equipment, each of the leaf nodes 106a-106 h can recover the respective data D1-D8 from the optical signalreceived from the second optical path 108 b (e.g., by demodulating theoptical signal received over that optical path, in particular theoptical subcarrier that was assigned to or allotted to that leaf node.Accordingly, the connectivity between the hub node 104 and each of theleaf network 106 a-106 n can be maintained, despite malfunctioningoptical links or equipment.

Further, each of the leaf nodes 106 a-106 n also can be configured totransmit multiple instances of a particular portion of data to the hubnode 104 concurrently using the optical paths 108 a and 108 b. Forinstance, each of the leaf nodes 106 a-106 h can receive respective dataD1′-D8′ intended for the hub node 104. Each of the leaf nodes 106 a-106h can generate a first optical signal, modulate the first optical signalbased on a respective one of the data D1′-D8′ (e.g., using respectiveoptical subcarriers assigned to or allotted to the leaf nodes 106 a-106h), and transmit the first optical signal over the second optical path108 b. With reference to this data transmission, the second optical path108 b may be referred to as the “leaf working Tx” path or the “hubworking Rx” path.

Further, each of the leaf nodes 106 a-106 h can generate a secondoptical signal, modulate the second optical signal based on a respectiveone of the data D1′-D8′ (e.g., using respective optical subcarriersassigned to or allotted to the leaf nodes 106 a-106 h), and transmit thesecond optical signal over the first optical path 108 a, concurrentlywith the transmission of the first optical signal over the secondoptical path 108 b. With reference to this data transmission, the firstoptical path 108 a may be referred to as the “leaf protect Tx” path orthe “hub protect Rx” path.

Similarly, in some implementations, the information transmitted by aleaf node 106 a-106 h along the first optical path 108 a can beidentical to the information transmitted by the leaf node 106 a-106 halong the second optical path 108 b.

In some implementations, the information transmitted by a leaf node 106a-106 h along the first optical path 108 can be different from theinformation transmitted by the leaf node 106 a-106 h along the secondoptical path 108 b. For example, the first information and the secondinformation can include the same data modulated according to differentdigital subcarriers (e.g., as described above). As another example, thefirst information and the second information can include the same datatransmitted according to different forward error correction (FEC)schemes (e.g., by including different FEC codes or bits). For instance,as shown in FIG. 2A, the length of the first optical path 108 a from theleaf node 106 b to the hub node 104 (e.g., 40 km) can be different fromthe length of the second optical path 108 b from the leaf node 106 b tothe hub node 104 (60 km). Due to this difference, the leaf node 106 bcan transmit data intended to the hub node 104 according to differentFEC schemes (e.g., by including different FEC codes or bits), dependingon the optical path this is used.

Similarly, during normal operation (e.g., when both the first opticalpath 108 a and the second optical path 108 b are intact and do not haveany malfunctioning optical links or equipment), the hub node 104 canrecover the data D1′-D8′ from the optical signal received from thesecond optical path 108 b (e.g., by demodulating the optical signalreceived over that optical path, in particular the optical subcarriersthat are assigned to or allotted to each of the leaf nodes). Forexample, referring to FIG. 2A, the hub node 104 can recover the dataD1′-D8′.

However, if the second optical path 108 b includes severed ormalfunctioning optical links or equipment, the hub node 104 can recoverthe data D1′-D8′ from the optical signal received from the first opticalpath 108 a (e.g., by demodulating the optical signal received over thatoptical path, in particular the optical subcarriers that are assigned toor allotted to each of the leaf nodes). Accordingly, the connectivitybetween the hub node 104 and each of the leaf network 106 a-106 n can bemaintained, despite malfunctioning optical links or equipment.

As described above, each of the nodes can modulate an optical signaldifferently, depending on the intended destination of the data that isbeing transmitted. Further, each of the nodes can modulate an opticalsignal differently, depending on the optical path along which theoptical signal is to be conveyed. The modulation of optical signals isdescribed in greater detail with respect to FIG. 2B.

Referring to FIG. 2B, the hub node 104 can be configured to transmit andreceive data from each of the leaf nodes 106 a-106 h. Further, each ofthe leaf nodes 106 a-106 h is assigned respective optical subcarriersfor transmitting and receiving data. For instance, a set of opticalsubcarriers SC1-SC16 and SC1′-SC′16 may be made available for use by theoptical communication system 100 (e.g., as shown in FIG. 3 ), and eachleaf node 106 a-106 h can be assigned respective optical subcarriersfrom the set for use. In this example, the leaf node 106 a is assignedoptical subcarriers SC1 and SC9 for receiving data, and opticalsubcarriers SC1′ and SC9′ for transmitting data. Further, the leaf node106 b is assigned optical subcarriers SC2 and SC10 for receiving data,and optical subcarriers SC2′ and SC2′ for transmitting data. Further,the leaf node 106 h is assigned optical subcarriers SC8 and SC16 forreceiving data, and optical subcarriers SC8′ and SC16′ for transmittingdata.

The hub node 104 can transmit data to each of the leaf nodes 106 a-106 husing the optical paths 108 a and 108 b of the access ring 102. Forexample, the hub node 104 can transmit a first instance of the data D1to the leaf node 106 a by generating a first optical signal, modulatingthe first optical signal based on the data D1 using the opticalsubcarrier SC1, and transmitting the optical signal to the leaf node 106a using the first optical path 108 a. Further, the hub node 104 can alsotransmit a second instance of the data D1 to the leaf node 106 a,concurrently with the transmission of the first instance of the data D1,by generating a second optical signal, modulating the second opticalsignal based on the data D1 using the optical subcarrier SC9, andtransmitting the optical signal to the leaf node 106 a using the secondoptical path 108 b.

The leaf node 106 a can retrieve the data D1 by monitoring the firstoptical path 108 a for optical signals, and demodulating any opticalsignals received along the first optical path 108 a with respect to theoptical subcarrier SC1. Further, the leaf node 106 a can also retrievethe data D1 by monitoring the second optical path 108 b for opticalsignals, and demodulating any optical signals received along the secondoptical path 108 b with respect to the optical subcarrier SC9. Duringnormal operation (e.g., when both the first optical path 108 a and thesecond optical path 108 b are intact and do not have any malfunctioningoptical links or equipment), the leaf node 106 a will receive multipleoptical signals from the optical paths, each having a respectiveinstance of the same data D1. The leaf node 106 a can selectivelyrecover the data D1 from the optical signal received over one of theoptical paths (e.g., the first optical path 108 a), and discard orotherwise ignore the optical signal received over the other optical path(e.g., the second optical path 108 b).

The hub node 104 can transmit data to each of the other leaf nodes 106b-106 h using a similar manner as described above, but using the opticalsubcarriers assigned to each of the leaf nodes 106 b-106 h instead. Forexample, the hub node 104 can transmit a first instance of the data D2to the leaf node 106 b by generating a first optical signal, modulatingthe first optical signal based on the data D2 using the opticalsubcarrier SC2, and transmitting the optical signal to the leaf node 106b using the first optical path 108 a. Further, the hub node 104 can alsotransmit a second instance of the data D2 to the leaf node 106 b,concurrently with the transmission of the first instance of the data D2,by generating a second optical signal, modulating the second opticalsignal based on the data D2 using the optical subcarrier SC10, andtransmitting the optical signal to the leaf node 106 b using the secondoptical path 108 b.

Each of the leaf nodes 106 b-106 h can retrieve data from the hub node104 in a similar manner as described above, but using the opticalsubcarriers assigned to each of the leaf nodes 106 b-106 h instead. Forexample, the leaf node 106 b can retrieve the data D2 by monitoring thefirst optical path 108 a for optical signals, and demodulating anyoptical signals received along the first optical path 108 a with respectto the optical subcarrier SC2. Further, the leaf node 106 b can alsoretrieve the data D2 by monitoring the second optical path 108 b foroptical signals, and demodulating any optical signals received along thesecond optical path 108 b with respect to the optical subcarrier SC10.During normal operation (e.g., when both the first optical path 108 aand the second optical path 108 b are intact and do not have anymalfunctioning optical links or equipment), the leaf node 106 b willreceive multiple optical signals from the optical paths, each having arespective instance of the same data D2. The leaf node 106 b canselectively recover the data D2 from the optical signal received overone of the optical paths (e.g., the first optical path 108 a), anddiscard or otherwise ignore the optical signal received over the otheroptical path (e.g., the second optical path 108 b).

Further, each of the leaf nodes 106 a-106 h can also transmit data tothe hub node 104 using the optical paths 108 a and 108 b of the accessring 102. For example, the leaf node 106 a can transmit a first instanceof the data D1′ to the hub node 104 by generating a first opticalsignal, modulating the first optical signal based on the data D1′ usingthe optical subcarrier SC1′, and transmitting the optical signal to thehub node 104 using the second optical path 108 b. Further, the leaf node106 a can also transmit a second instance of the data D1′ to the hubnode 104, concurrently with the transmission of the first instance ofthe data D1′, by generating a second optical signal, modulating thesecond optical signal based on the data D1′ using the optical subcarrierSC9′, and transmitting the optical signal to the hub node 104 using thefirst optical path 108 a.

The hub node 104 can retrieve the data D1′ by monitoring the secondoptical path 108 b for optical signals, and demodulating any opticalsignals received along the second optical path 108 b with respect to theoptical subcarrier SC1′. Further, the hub node can also retrieve thedata D1′ by monitoring the first optical path 108 a for optical signals,and demodulating any optical signals received along the first opticalpath 108 a with respect to the optical subcarrier SC9′. During normaloperation (e.g., when both the first optical path 108 a and the secondoptical path 108 b are intact and do not have any malfunctioning opticallinks or equipment), the hub node will receive multiple optical signalsfrom the optical paths, each having a respective instance of the samedata D1′. The hub node 104 can selectively recover the data D1′ from theoptical signal received over one of the optical paths (e.g., the secondoptical path 108 b), and discard or otherwise ignore the optical signalreceived over the other optical path (e.g., the first optical path 108a).

Each of the other leaf nodes 106 b-106 h can transmit data to the hubnode 104 using a similar manner as described above, but using theoptical subcarriers assigned to each of the leaf nodes 106 b-106 hinstead. For example, the leaf node 106 b can transmit a first instanceof data D2′ to the hub node 104 by generating a first optical signal,modulating the first optical signal based on the data D2′ using theoptical subcarrier SC2′, and transmitting the optical signal to the hubnode 104 using the second optical path 108 b. Further, the leaf node 106b can also transmit a second instance of the data D2′ to the hub node104, concurrently with the transmission of the first instance of thedata D2′, by generating a second optical signal, modulating the secondoptical signal based on the data D2′ using the optical subcarrier SC10′,and transmitting the optical signal to the hub node 104 using the firstoptical path 108 a.

The hub node 104 can retrieve data from each of the leaf nodes 106 b-106h the hub node 104 in a similar manner as described above, but using theoptical subcarriers assigned to each of the leaf nodes 106 b-106 hinstead. For example, the hub node 104 can retrieve the data D2′ bymonitoring the second optical path 108 b for optical signals, anddemodulating any optical signals received along the second optical path108 b with respect to the optical subcarrier SC2′. Further, the leafnode 106 b can also retrieve the data D2′ by monitoring the firstoptical path 108 a for optical signals, and demodulating any opticalsignals received along the first optical path 108 a with respect to theoptical subcarrier SC10′. During normal operation (e.g., when both thefirst optical path 108 a and the second optical path 108 b are intactand do not have any malfunctioning optical links or equipment), the hubnode 104 will receive multiple optical signals from the optical paths,each having a respective instance of the same data D2′. The hub node 104can selectively recover the data D2′ from the optical signal receivedover one of the optical paths (e.g., the second optical path 108 b), anddiscard or otherwise ignore the optical signal received over the otheroptical path (e.g., the first optical path 108 a).

In some implementations, multiple optical signals can be transmitted bythe nodes of the optical communications system 100 concurrently. Forexample, each of the nodes can receive optical signals along an opticalpath (e.g., from one or more other nodes preceding it in the access ring102), and inject additional optical signals into the optical path (e.g.,by multiplexing and/or superimposing the optical signals). For example,referring to FIG. 2B, the leaf node 106 a can receive, from the firstoptical path 108 a, optical signals having data modulated according tothe optical subcarriers SC1-SC8 (e.g., corresponding to data transmittedby the hub node 104 to the leaf nodes 106 a-106 h, respectively). Theleaf node 106 a can inject an additional optical signal into the firstoptical path 106 a (e.g., an optical signal having data modulatedaccording to the optical subcarrier SC9′), such that the optical signaloutput from the leaf node 106 a includes data modulated according to theoptical subcarriers SC1-SC8 and SC9′.

FIG. 3 shows example sets of optical subcarriers SC1-SC16 and SC1′-SC′16that may be made available for use by the optical communication system100. In this example, the optical subcarriers SC1-SC16 are used totransmit data from the hub node 104 to the leaf nodes 106 a-106 h, andthe optical subcarriers SC1′-SC16′ are used to transmit data from theleaf nodes 106 a-106 h to the hub node 104. Further, the opticalsubcarriers SC1-SC8 are used to transmit data according to one opticalpath (e.g., the first optical path 108 a, the “hub working Tx” path),whereas the optical subcarriers SC9-SC16 are used to transmit dataaccording to the other optical path (e.g., the second optical path 108b, the “hub protect Tx” path). Similarly, the optical subcarriersSC1′-SC8′ are used to transmit data according to one optical path (e.g.,the second optical path 108 b, the “leaf working Tx” path), whereas theoptical subcarriers SC9′-SC16′ are used to transmit data according tothe other optical path (e.g., the first optical path 108 a, the “leafprotect Tx” path).

In the example shown in FIG. 3 , each of the optical subcarriers do notspectrally overlap one another in the frequency domain. Further, thesubsets of optical subcarriers that are used by the hub node 104 totransmit data along different respective optical paths are spectrallycontinuous with one another, and do not spectrally overlap one anotherin the frequency domain. Further, the subsets of optical subcarriersthat are used by the hub node 104 to transmit data along differentrespective optical paths are spectrally separated from one another inthe frequency domain by a guard band 300 a (e.g., a gap in the frequencydomain). Further, the subsets of optical subcarriers that are used bythe leaf nodes 106 a-106 h to transmit data along different respectiveoptical paths are separated from one another in the frequency domain bya guard band 300 b (e.g., a gap in the frequency domain). A guard bandcan be useful, for example, to eliminate or otherwise reduce signalinterference between the different sets of optical subcarriers.

In some implementations, a guard band can be implemented by selectively“blocking” the optical subcarriers that are located spectrally betweenthe two sets of optical subcarriers in the frequency domain. Forexample, if the subcarriers SC1 to SC16 are contiguous in the frequencydomain, the optical subcarriers SC8 and SC9 can be “blocked,” theoptical subcarriers SC1 to SC7 can be used to transmit data along oneoptical path, and the optical subcarriers SC10 to SC16 can be used totransmit data along another optical path. In practice, the width of theguard band (e.g., the number of “blocked” optical subcarriers”) canvary, depending on the implementation.

In some implementations, a guard band can be implemented by adjustingthe frequency of the optical subcarriers, such that a frequency gap isformed between two sets of optical subcarriers in the frequency domain.For example, if the optical subcarriers SC1 to SC8 are used to transmitdata along one optical path and the optical subcarriers SC9 to SC16 areused to transmit data along another optical path, the opticalsubcarriers SC1 and SC16 can be assigned different respectivefrequencies such that there is a frequency gap between the opticalsubcarriers SC8 and SC9. In practice, the width of the guard band (e.g.,the frequency range of the guard band) can vary, depending on theimplementation.

Additional details regarding selectively blocking optical subcarriersand/or selectively forming frequency gaps between optical subcarriersare described in further detail below.

Although FIG. 3 shows an example configuration of optical subcarriers,this is merely an illustrative example. In practice, any number ofoptical subcarriers can be used by each of the network nodes to transmitand/or receive data using the optical communications system 100.Further, although FIG. 3 shows an example configuration is which equalnumbers of optical subcarriers are allotted for the transmission and/orreception of data along each of the optical paths, in practice, adifferent respective number of optical subcarriers are can allotted forthe transmission and/or reception of data along different respectiveoptical paths.

As an example, in some implementations, a subset of six opticalsubcarriers can allotted for the transmission and/or reception of dataalong a first optical path, and a subset of ten optical subcarriers canbe allotted for the transmission and/or reception of data along a secondoptical path (with a guard band between the subsets of opticalsubcarriers).

As another example, in some implementations, four optical subcarrierscan allotted for the transmission and/or reception of data along a firstoptical path, and twelve optical subcarriers can be allotted for thetransmission and/or reception of data along a second optical path (witha guard band between the subsets of optical subcarriers).

As another example, in some implementations, a subset of eight opticalsubcarriers can allotted for the transmission and/or reception of dataalong a first optical path, some of which are not continuous with oneanother. Further, a subset of eight optical subcarriers can be allottedfor the transmission and/or reception of data along a second opticalpath, some of which are not continuous with one another. For instance,optical subcarriers can be allotted for the transmission and/orreception of data along the optical paths according to an alternatingpattern (e.g., the optical subcarriers SC1, SC3, SC5, . . . , etc. canbe allotted for the transmission and/or reception of data along one ofthe optical paths, and the optical subcarriers SC2, SC4, SC6, . . . ,etc. can be allotted for the transmission and/or reception of data alongthe other one of the optical paths).

FIG. 4A shows an example of a hub node 104 in greater detail.

During an example data transmission operation of the hub node 104, a Txprocessor 450 of the hub node 104 receives optical data D1 to D8(intended for the leaf nodes 106 a-106 h, respectively) using an opticalsignal processor (DSP) 402. The data D1 to D8 is transmitted from theDSP 402 to an optical to analog converter (D/A) 404 (which also may bereferred to as a digital-to-analog conversion circuitry). The D/A 404converts the optical data into corresponding analog signal. The analogsignals are provided to a laser driver 406 (which may also be referredto as driver circuitry). The driver 406 generates optical signals basedon the analog signals. The generated optical signals are provided to amodulator 408, which modulates the optical signal with a carrier opticalsignal output by a laser 410 and an optical splitter 412. As an example,the modulated optical signal can include data modulated according toeach of the optical subcarriers SC1 to SC16.

The modulated optical signal is provided to an optical splitter 414,which splits the modulated optical signal between two wavelengthselective switches (WSSes) 416 a and 416 b (e.g., splits the modulatedoptical signal, such that the power of the optical signal is split amongthe WSSes 416 a and 416 b). The WSS 416 a selects wavelengths of themodulated optical signal corresponding to a subset of the opticalsubcarriers (e.g., the optical subcarriers SC1-SC8), and injects theselected wavelengths of the modulated optical signal into the firstoptical signal path 108 a (e.g., the “hub working Tx” path). The otherWSS 416 b selects wavelengths of the modulated optical signalcorresponding to the other subset of the optical subcarriers (e.g., theoptical subcarriers SC9-SC16), and injects the selected wavelengths ofthe modulated optical signal into the second optical signal path 108 b(e.g., the “hub protect Tx” path).

During an example data receipt operation of the hub node 104, the hubnode 104 receives a first optical signal from the first optical path 108a (e.g., the “hub protect Rx” path) using a WSS 416 c, and receives asecond optical signal from the second optical path 108 b (e.g., the “hubworking Tx” path) using a WSS 416 d. The first optical signal caninclude, for example, a first instance of data D1′-D8′ transmitted bythe leaf nodes 106 a-106 h, respectively. Further, the second opticalsignal can include a second instance of the data D1′-D8′ transmitted bythe leaf nodes 106 a-106 h, respectively. The WSS 416 c selectswavelengths of the first optical signal corresponding to a subset of theoptical subcarriers (e.g., the optical subcarriers SC9′-SC16′), andprovides the selected wavelengths to an optical combiner 420. Similarly,the WSS 416 d selects wavelengths of the second optical signalcorresponding to another subset of the optical subcarriers (e.g., theoptical subcarriers SC1′-SC8′), and provides the selected wavelengths tothe optical combiner 418.

The optical combiner 418 combines the selected wavelengths of light, andprovides the combined wavelengths of light to one or more polarizationbeam splitters (PBSes) 420 of an Rx processor 452. The one or more PBSes420 split the received light into different portions based on theirpolarization state (e.g., into TE and TM components), and provides thelight to one or more optical hybrids 422 (which also may be referred toas optical hybrid circuitry). The one or more optical hybrids 422demodulate the received wavelengths of light (e.g., based on a carriersignal provided by the laser 410 and the optical splitter 412), andoutputs the demodulated light to a photodetector (PD) 424 (which mayalso be referred to as photodetector circuitry 424). The PD 424generates electrical signals based on the received light. The electricalsignals are provided to a trans-impedance amplifier (TIA) 426. The TIA426 amplifies the received electrical signals, and provides theamplified electrical signals to an analog to an analog-to-digitalconverter (A/D) 428 (which may also be referred to as analog-to-digitalconversion circuitry). The A/D 428 converts the amplified electricalsignals to optical signals, and provides the optical signals to a DSP42430. The DSP 430 processes the optical signals, and outputs the dataD1′-D8′.

Although FIG. 4A shows an example hub node 104 having four WSSes 416a-416 d, in some implementations, a hub node 104 can include a fewernumber of WSSes. For example, referring to FIG. 4B, a hub node 104 caninclude two WSSes 416 e and 416 f. The WSS 416 e can be configured toselect wavelengths of light for transmission using the optical path 108a, and to select wavelengths of light received from the optical path 108b. The WSS 416 f can be configured to select wavelengths of light fortransmission using the optical path 108 b, and to select wavelengths oflight received from the optical path 108 a.

As described above, during normal operation (e.g., when both the firstoptical path 108 a and the second optical path 108 b are intact and donot have any malfunctioning optical links or equipment), each of theleaf nodes 106 a-106 h can recover the respective data D1-D8 from theoptical signal received from the first optical path 108 a (e.g., bydemodulating the optical signal received over that optical path, inparticular the optical subcarrier that was assigned to or allotted tothat leaf node). For example, the leaf node 106 a can recover the dataD1, the leaf node 106 b can recover the data D2, and so forth.Similarly, the hub node 104 can recover the data D1′-D8′ from theoptical signal received from the second optical path 108 b (e.g., bydemodulating the optical signal received over that optical path, inparticular the optical subcarriers that are assigned to or allotted toeach of the leaf nodes). For example, the hub node 104 can recover thedata D D8′.

As an illustrative example, the leaf node 106 b is shown in greaterdetail in FIG. 5 . During an example data receipt operation of the leafnode 106 b, the leaf node 106 b receives a first optical signal from thefirst optical path 108 a (e.g., the “hub working Tx” path) at a WSS 502a. The WSS 502 a selects the wavelengths of the optical signalcorresponding to the subset of optical subcarriers used by the hub node104 to transmit data along the first optical path 108 a (e.g. SC1 toSC8), and provides the selected wavelengths to an optical combiner 504.Further, the leaf node 106 b receives a second optical signal from thesecond optical path 108 b (e.g., the “hub protect Tx” path) at a WSS 502b. The WSS 502 b selects the wavelengths of the optical signalcorresponding to another subset of optical subcarriers used by the hubnode 104 to transmit data along the second optical path 108 b (e.g. SC9to SC16), and provides the selected wavelengths to the optical combiner504. The optical combiner 504 combines the selected wavelengths, andprovides the selected wavelengths to an Rx processor 506. The Rxprocessor 506 can be similar to the Rx processor 452 shown in FIG. 4A.The Rx processor 506 retrieves the data intended for the leaf node 106 b(e.g., the data D2), and outputs the retrieved data for furtherprocessing. As an example, the Rx processor 506 can selectivelydemodulate the optical signal received from the optical combiner 504according to the optical subcarriers SC2 and/or SC10 (e.g., to recoverdata D2), and discard or otherwise ignore the other portions of theoptical signal. In some implementations, if the same instance of data isreceived using both of the optical subcarriers SC2 and SC10, the Rxprocessor 506 can select the instance of data received using one of theoptical subcarriers (e.g., SC2, over the “hub working Tx” path), anddiscard or otherwise ignore the instance of the data received using theother optical subcarrier (e.g., SC10, over the “hub protect Tx” path).

Further, during an example data transmission operation of the leaf node106 b, the leaf node 106 b receives optical data D2′ (intended for thehub node 104) using a Tx processor 508. The Tx processor 508 can besimilar to the Tx processor 450 shown in FIG. 4A. The Tx processor 508generates an optical signal in which the data D2′ is modulated accordingto the optical subcarriers SC2′ and SC10′, and provides the opticalsignal to an optical splitter 510. The optical splitter splits theoptical signal between a WSS 502 c and a WSS 502 d. The WSS 502 cselects wavelengths of light corresponding to one of the opticalsubcarriers used by the leaf node 106 b to transmit data (e.g., theoptical subcarrier SC2′), and injects the selected wavelengths of lightinto the second optical path 108 b (e.g., the “hub working Rx” path).The WSS 502 d selects wavelengths of light corresponding to the otherone of the optical subcarriers used by the leaf node 106 b to transmitdata (e.g., the optical subcarrier SC10′), and injects the selectedwavelengths of light into the first optical path 108 a (e.g., the “hubprotect Rx” path).

The hub node 104 can retrieve the data D2′ based on the optical signalsreceived from the optical path 108 a and/or the optical path 108 b(e.g., as described with respect to FIG. 4A). In some implementations,if the same instance of data is received using both of the opticalsubcarriers SC2′ and SC10′, the hub node 104 can select the instance ofdata received using one of the optical subcarriers (e.g., SC2′, over the“hub working Rx” path), and discard or otherwise ignore the instance ofthe data received using the other optical subcarrier (e.g., SC10′, overthe “hub protect Rx” path).

However, if the first optical path 108 a and/or the second optical path108 b include severed or malfunctioning optical links or equipment, oneor more of the hub node 104 and/or the leaf nodes 106 a-106 h may not beable to receive optical signals in the manner described above. Forexample, referring to FIG. 6 , if the first optical path 108 a and thesecond optical path 108 b are severed between the leaf nodes 106 a and106 b (e.g., a “fiber cut” occurs between the leaf nodes 106 a and 106b), the leaf node 106 b may be unable to receive optical signals alongthe first optical path 108 a. Further, optical signals transmitted bythe leaf node 106 b along the second optical path 108 b may not reachthe leaf node 106 a or the hub node 104.

As described above, the leaf nodes 106 a-106 h can be configured tomitigate the effects of a severed optical link in the access ring 102.For example, if the first optical path 108 a and the second optical path108 b are severed between the leaf nodes 106 a and 106 b, the leaf node106 b may be unable to receive optical signals along the first opticalpath 108 a (e.g., no data is received from the “hub working Tx” path).However, the leaf node 106 b can continue to receive optical signalsfrom the second optical path 108 b (e.g., the “hub protect Tx” path),and extract the data D2 from the received optical signal.

As another example, if the first optical path 108 a and the secondoptical path 108 b are severed between the leaf nodes 106 a and 106 b,the hub node 104 may be unable to receive optical signals from the leafnode 106 b along the second optical path 108 b (e.g., no data isreceived from the leaf node 1086 from the “hub working Rx” path).However, the hub node 104 can continue to receive optical signals fromthe leaf node 106 b from the first optical path 108 a (e.g., the “hubprotect Rx” path), and extract the data D2′ from the received opticalsignal.

As described above, in some implementations, the first optical path 108a and/or the second optical path 108 b may include malfunctioningoptical links or equipment that enable optical signals to be conveyedbetween network nodes, but in a degraded form. For example, the opticalsignals exhibit a particular degree of attenuation, contain a particularamount of noise or other interference, or exhibit other characteristicsthat may make it more difficult to recover the data. In this situation,a network node can receive a second optical signal from another opticalpath (e.g., a “protection” path), compare the characteristics of theoptical signals received from each optical path, and select one of theoptical signals for further processing (e.g., based on an estimatedquality of each of the optical signals). Accordingly, the connectivitybetween the first network node and the second network node can bemaintained, despite malfunctioning optical links or equipment.

For example, if the first optical path 108 a and the second optical path108 b include malfunctioning optical links or equipment between the leafnodes 106 a and 106 b, the leaf node 106 b may receive degraded opticalsignals along the first optical path 108 a. However, the leaf node 106 bcan continue to receive optical signals from the second optical path 108b (e.g., the “hub protect Tx” path). The leaf node 106 b can compare thecharacteristics of optical signals received from each optical path,select one of the optical signals based on the comparison, and extractthe data D2 from the selected optical signal. In some implementations,optical signals can be selected based on a measured or estimated latencyassociated with each of the optical signals (e.g., a latency associatedwith transmitting the optical signal from the hub node 104 to the leafnode 106 b), a pre-forward error correction quality factor (pre-FEC Q)associated with each of the optical signals, one or more other factors,or any combination thereof. For example, optical signals having a lowerlatency and/or a higher pre-FEC Q may be selected over optical signalshaving a higher latency and/or a lower pre-FEC Q.

As another example, if the first optical path 108 a and the secondoptical path 108 b include malfunctioning optical links or equipmentbetween the leaf nodes 106 a and 106 b, the hub node 104 may receivedegraded optical signals along the second optical path 108 b. However,the hub node 104 can continue to receive optical signals from the firstoptical path 108 a (e.g., the “hub protect Rx” path) concurrently withthe optical signals along the second optical path 108 b. The hub node104 can compare the characteristics of optical signals received fromeach optical path, select one of the optical signals based on thecomparison, and extract the data D2′ from the selected optical signal.In some implementations, optical signals can be selected based on ameasured or estimated latency associated with each of the opticalsignals (e.g., a latency associated with transmitting the optical signalfrom the leaf node 106 b to the hub node 104), a pre-FEC Q associatedwith each of the optical signals, one or more other factors, or anycombination thereof. For example, optical signals having a lower latencyand/or a higher pre-FEC Q may be selected over optical signals having ahigher latency and/or a lower pre-FEC Q.

In some implementations, a leaf node 106 a-106 h can preferentiallyselect optical signals transmitted by a source node (e.g., a hub 104)along a primary optical path having a shorter length from the sourcenode to the leaf node 106 a-106 h, over optical signals transmitted bythe source node along a secondary optical path having a longer lengthbetween the source node and the leaf node 106 a-106 h. Upon detecting anerror in the reception of data along the primary optical path at aparticular point in a data stream (e.g., an absence of data and/or thereception of degraded data due to a fiber cut or other malfunction), theleaf node 106 a-106 h can retrieve the remaining portion of the datastream from the secondary optical path instead. Accordingly, the leafnode 106 a-106 h can seamlessly retrieve data in a “hitless” matter,without the loss of data.

As an example, referring back to FIG. 2A, the length of the firstoptical path 108 a from the hub node 104 to the leaf node 106 b (e.g.,60 km) can be longer than the length of the second optical path 108 bfrom the hub node 104 and to leaf node 106 b (40 km). Due to thisdifference, the leaf node 106 b can preferentially select opticalsignals transmitted by the hub node 104 along the second optical path108 b, over the optical signals transmitted along the first optical path108 a (e.g., by demodulating the optical signals received from thesecond optical path 108 b to recover a stream of data packets 1 to N).Upon detecting an error in the reception of data along the secondoptical path 108 b at a particular point of time (e.g., a data packetN+1 was not received the second optical path 108 b within an expectedtime frame, or a degraded version of the data packet N+1 was receivedfrom the second optical path 108 b), the leaf node 106 b can retrievethe remaining portion of the data stream (data packets N+1, N+2, . . .etc.) from the first optical path 108 a instead. Due to the differencesin the length of the first optical paths 108 a and 108 b between the twonodes, the data that is transmitted by the hub node 104 to the leaf node106 b along the first optical path 108 a is delayed relative to the datathat is transmitted by the hub node 104 to the leaf node 106 b along thesecond optical path 108 b. This enables the leaf node 106 b to switchfrom retrieving data from the second optical path 108 b to the firstoptical path 108 a upon to detection of an error, without missing anydata in the data stream.

A similar technique can be used by a hub node to receive a stream ofdata packets from a leaf node. For example, a hub node can selectoptical signals transmitted by a leaf node along a primary optical pathhaving a shorter length from leaf node to the hub node, over opticalsignals transmitted by the leaf node to the hub node along a secondaryoptical path having a longer length between the hub leaf node and thehub node. Upon detecting an error in the reception of data along theprimary optical path at a particular point in a data stream (e.g., anabsence of data and/or the reception of degraded data due to a fiber cutor other malfunction), the hub node can retrieve the remaining portionof the data stream from the secondary optical path instead.

In some implementations, a destination node can store data packetsreceived from each of the optical paths in a respective data buffer.Further, the destination node can preferentially select, from the databuffers, data packets received from a primary optical path having ashorter length from the source node to the destination node, over datapackets received from a secondary optical path having a longer lengthbetween the source node and the destination node. Upon detecting anerror in the reception of data along the primary optical path at aparticular point in a data stream (e.g., an absence of data and/or thereception of degraded data due to a fiber cut or other malfunction), thedestination node can retrieve the remaining portion of the data streamfrom the secondary optical path instead.

This can be beneficial, for example, in implementations where thelengths of the optical paths between the source node and the destinationnode are similar or equal. For instance, in these implementations, thedelay between the data streams received from the optical paths may beshorter than the time needed by the destination node to (i) detect anerror in the transmission of the earlier data stream, and (ii) switch toretrieving data from the delayed data stream directly. In theseimplementations, (i) detect an error in the transmission of the earlierdata stream, and (ii) retrieve a buffered version of the delayed datastream instead, such that no data is missed.

As described above, in some implementations, a network node can transmitmultiple instances of the same data concurrently using multipledifferent optical paths. However, in some implementations, a networknode can transmit one instance of data using one optical path. If afault is detected in that optical path (e.g., the optical path isdetermined to have been severed or otherwise disrupted), the networknode can transmit a second instance of the same data using a differentoptical path.

As an illustrative example, an example data receipt operation of theleaf node 106 b is shown in FIGS. 7A and 7B. In general, one or more ofthe components shown in FIGS. 7A and 7B can be similar to those shown inFIG. 5 .

As shown in FIG. 7A, during normal operation (e.g., when both the firstoptical path 108 a and the second optical path 108 b are intact and donot have any malfunctioning optical links or equipment), the leaf node106 b receives optical data D2′ (intended for the hub node 104) using aTx processor 508. The Tx processor 508 can be similar to the Txprocessor 450 shown in FIG. 4A. The Tx processor 508 generates anoptical signal in which the data D2′ is modulated according to theoptical subcarrier SC2′, and provides the optical signal to the opticalsplitter 510. The optical splitter splits the optical signal between theWSS 502 c and the WSS 502 d. The WSS 502 c selects wavelengths of lightcorresponding to the optical subcarrier SC2′, and injects the selectedwavelengths of light into the second optical path 108 b (e.g., the “hubworking Rx” path). The WSS 502 d selectively blocks the wavelengths oflight corresponding to the optical subcarrier SC2′, such that it is notinjected into the first optical path 108 a (e.g., the “hub protect Rx”path). Accordingly, the leaf node 106 b will not interfere with theoptical signals received from the first optical path 108 a, particularlythe portion of the optical signal corresponding to the opticalsubcarrier SC2 generated by the hub node 104.

As described above, if the first optical path 108 a and/or the secondoptical path 108 b include severed or malfunctioning optical links orequipment, one or more of the hub node 104 and/or the leaf nodes 106a-106 h may not be able to receive optical signals in the mannerdescribed above. For example, referring back to FIG. 6 , if the firstoptical path 108 a and the second optical path 108 b are severed betweenthe leaf nodes 106 a and 106 b (e.g., a “fiber cut” occurs between theleaf nodes 106 a and 106 b), any optical signals transmitted by the leafnode 106 b along the second optical path 108 b may not reach the leafnode 106 a or the hub node 104.

Referring to FIG. 7B, to maintain connectivity with the hub node 104,the Tx processor 508 generates an optical signal in which the data D2′is modulated according to the optical subcarrier SC10′, and provides theoptical signal to the optical splitter 510. The optical splitter splitsthe optical signal between the WSS 502 c and the WSS 502 d. The WSS 502d selects wavelengths of light corresponding to the optical subcarrierSC10′, and injects the selected wavelengths of light into the firstoptical path 108 a (e.g., the “hub protect Rx” path). The WSS 502 cselectively blocks the wavelengths of light corresponding to the opticalsubcarrier SC10′, such that it is not injected into the second opticalpath 108 b (e.g., the “hub protect Rx” path). Accordingly, the hub node104 can continue to receive an instance of the data D2′ from the leafnode 106 b, despite a fiber cut in the access ring 102.

Although FIGS. 5, 7A, and 7B show an example leaf node 106 b having fourWSSes 502 a-502 d, in some implementations, a leaf node can include afewer number of WSSes. For example, referring to FIG. 7C, a leaf node106 b can include two WSSes 502 e and 502 f. The WSS 502 e can beconfigured to select wavelengths of light for transmission using theoptical path 108 b, and to select wavelengths of light received from theoptical path 108 a. The WSS 416 f can be configured to selectwavelengths of light for transmission using the optical path 108 a, andto select wavelengths of light received from the optical path 108 b.

In the examples shown above, a single hub node transmits and receivesdata from multiple leaf nodes. However, this need not be the case. Forexample, in some implementations, multiple hub nodes and transmit andreceive data from multiple leaf nodes.

An example optical communications system 100 having a dual hub nodeconfiguration is shown in FIG. 8 . In general, each of the componentsshown in FIG. 8 can be similar to those shown in FIGS. 2A and 2B.However, in this example, the optical communication system 100 includestwo hub nodes 104 a and 104 b instead of a single hub node 104, andsixteen leaf nodes 106 a-106 p instead of eight leaf nodes 106 a-106 h.

The two hub nodes 104 a and 104 b can coordinate with one another tosend data to the leaf nodes 106 h and/or to receive data from the leafnodes 106 a-106 p. For instance, each of the hub nodes 104 a and 104 bcan receive data intended for each of the leaf nodes 106 a-106 p (e.g.,sixteen portions of data D1-D16 intended for sixteen leaf nodes 106a-106 p, respectively). The first hub node 104 a can generate a firstoptical signal, modulate the first optical signal based on the dataD1-D16 (e.g., using respective optical subcarriers assigned to orallotted to the leaf nodes 106 a-106 p in a first channel “Ch1,” SC1-1to SC16-1), and transmit the first optical signal over the first opticalpath 108 a (the “hub working Tx” path or the “leaf working Rx” path).

Further, the second hub node 104 b can generate a second optical signal,modulate the second optical signal based on the data D1-D16 (e.g., usingrespective optical subcarriers assigned to or allotted to the leaf nodes106 a-106 p in a second channel “Ch 2,” SC1-2 to SC16-2), and transmitthe second optical signal over the second optical path 108 b (the “hubprotect Tx” path or the “leaf protect Rx” path”), concurrently with thetransmission of the first optical signal over the optical path 108 a. Inthis manner, two hub nodes are used to transmit data concurrently to theleaf nodes 106 a-106 p along different respective optical paths, usingoptical subcarriers from two different channels.

In some implementations, the information transmitted by the first hubnode 104 a along the first optical path 108 a can be identical to theinformation transmitted by the second hub node 104 b along the secondoptical path 108 b.

In some implementations, the information transmitted by the first hubnode 104 a along the first optical path 108 a can be different from theinformation transmitted by the second hub node 104 along the secondoptical path 108 b. For example, the first information and the secondinformation can include the same data modulated according to differentdigital subcarriers (e.g., as described above). As another example, thefirst information and the second information can include the same datatransmitted according to different forward error correction (FEC)schemes (e.g., by including different FEC codes or bits). For instance,as shown in FIG. 8A, the length of the first optical path 108 a from thefirst hub node 104 a to the leaf node 106 b (e.g., 60 km) can bedifferent from the length of the second optical path 108 b from thesecond hub node 104 b and to leaf node 106 b (40 km). Due to thisdifference, the first hub node 104 a and the second hub node 104 b cantransmit data intended to the second leaf 106 b according to differentFEC schemes (e.g., by including different FEC codes or bits), dependingon the optical path this is used.

Further, the hub nodes 104 a and 104 b can receive data from the leafnodes 106 a-106 p along different respective optical paths. For example,each of the leaf nodes 106 a-106 p can receive respective data D1′-D16′intended for the hub node 104. Each of the leaf nodes 106 a-106 p cangenerate a first optical signal, modulate the first optical signal basedon a respective one of the data D1′-D16′ (e.g., using respective opticalsubcarriers assigned to or allotted to the leaf nodes 106 a-106 p in thefirst channel “Ch1,” SC1′-1 to SC16′-1), and transmit the first opticalsignal over the second optical path 108 b (e.g., the “leaf working Tx”path or the “hub working Rx” path). The first optical signal is receivedby the hub node 104 a, which demodulates the optical signal to retrievethe data D1′-D16′.

Further, each of the leaf nodes 106 a-106 h can generate a secondoptical signal, modulate the second optical signal based on a respectiveone of the data D1′-D16′ (e.g., using respective optical subcarriersassigned to or allotted to the leaf nodes 106 a-106 p in the secondchannel “Ch2,” SC1′-2 to SC16′-2), and transmit the second opticalsignal over the first optical path 108 a (“leaf protect Tx” path or the“hub protect Rx” path), concurrently with the transmission of the firstoptical signal over the second optical path 108 b. The second opticalsignal is received by the hub node 104 b, which demodulates the opticalsignal to retrieve the data D1′-D16′. In this manner, two hub nodes areused to receive data concurrently from the leaf nodes 106 a-106 p alongdifferent respective optical paths, using optical subcarriers from twodifferent channels.

In some implementations, the information transmitted by a leaf node 106a-106 h along the first optical path 108 a can be identical to theinformation transmitted by the leaf node 106 a-106 h along the secondoptical path 108 b.

In some implementations, the information transmitted by a leaf node 106a-106 h along the first optical path 108 can be different from theinformation transmitted by the leaf node 106 a-106 h along the secondoptical path 108 b. For example, the first information and the secondinformation can include the same data modulated according to differentdigital subcarriers (e.g., as described above). As another example, thefirst information and the second information can include the same datatransmitted according to different forward error correction (FEC)schemes (e.g., by including different FEC codes or bits). For instance,as shown in FIG. 8A, the length of the first optical path 108 a from theleaf node 106 b to the second hub node 104 b (e.g., 40 km) can bedifferent from the length of the second optical path 108 b from the leafnode 106 b to the first hub node 104 a (60 km). Due to this difference,the leaf node 106 b can transmit data intended to the first and secondhub nodes 104 a and 104 b according to different FEC schemes (e.g., byincluding different FEC codes or bits), depending on the optical paththis is used.

If the first optical path 108 a and/or the second optical path 108 binclude severed or malfunctioning optical links or equipment, one ormore of the hub nodes 104 a and 104 b and/or the leaf nodes 106 a-106 pmay not be able to receive optical signals in the manner describedabove. However, in a similar manner as described above, the componentsof the optical communication system 100 can be configured to mitigatethe effects of a severed optical link in the access ring 102. Forexample, if the first optical path 108 a and the second optical path 108b are severed between the leaf nodes 106 a and 106 b, the leaf node 106b may be unable to receive optical signals along the first optical path108 a (e.g., no data is received from the “hub working Tx” path).However, the leaf node 106 b can continue to receive optical signalsfrom the second optical path 108 b (e.g., the “hub protect Tx” path),and extract the data D2 from the received optical signal.

As another example, if the first optical path 108 a and the secondoptical path 108 b are severed between the leaf nodes 106 a and 106 b,the first hub node 104 a may be unable to receive optical signals fromthe leaf node 106 b along the second optical path 108 b (e.g., no datais received from the leaf node 1086 from the “hub working Rx” path).However, the second hub node 104 b can continue to receive opticalsignals from the leaf node 106 b from the first optical path 108 a(e.g., the “hub protect Rx” path), and extract the data D2′ from thereceived optical signal. In some implementations, the second hub node104 b can provide the data to the first hub node 104 a, such that italso has a record of the data.

Further, as described above, in some implementations, the first opticalpath 108 a and/or the second optical path 108 b may includemalfunctioning optical links or equipment that enable optical signals tobe conveyed between network nodes, but in a degraded form. For example,the optical signals exhibit a particular degree of attenuation, containa particular amount of noise or other interference, or exhibit othercharacteristics that may make it more difficult to recover the data. Inthis situation, a network node can receive a second optical signal fromanother optical path (e.g., a “protection” path), compare thecharacteristics of the optical signals received from each optical path,and select one of the optical signals for further processing (e.g.,based on an estimated quality of each of the optical signals).Accordingly, the connectivity between the first network node and thesecond network node can be maintained, despite malfunctioning opticallinks or equipment.

For example, if the first optical path 108 a and the second optical path108 b include malfunctioning optical links or equipment between the leafnodes 106 a and 106 b, the leaf node 106 b may receive degraded opticalsignals along the first optical path 108 a. However, the leaf node 106 bcan continue to receive optical signals from the second optical path 108b (e.g., the “hub protect Tx” path). The leaf node 106 b can compare thecharacteristics of optical signals received from each optical path,select one of the optical signals based on the comparison, and extractthe data D2 from the selected optical signal. In some implementations,optical signals can be selected based on a measured or estimated latencyassociated with each of the optical signals, a pre-FEC Q associated witheach of the optical signals, one or more other factors, or anycombination thereof. For example, optical signals having a lower latencyand/or a higher pre-FEC Q may be selected over optical signals having ahigher latency and/or a lower pre-FEC Q.

As another example, if the first optical path 108 a and the secondoptical path 108 b include malfunctioning optical links or equipmentbetween the leaf nodes 106 a and 106 b, the first hub node 104 a mayreceive degraded optical signals along the second optical path 108 b.However, the second hub node 104 b can continue to receive opticalsignals from the first optical path 108 a (e.g., the “hub protect Rx”path) concurrently with the first hub node 104 a receiving opticalsignals along the second optical path 108 b. The hub nodes 104 a and/or104 b can compare the characteristics of optical signals received fromeach optical path, select one of the optical signals based on thecomparison, and extract the data D2′ from the selected optical signal.In some implementations, optical signals can be selected based on ameasured or estimated latency associated with each of the opticalsignals, a pre-FEC Q associated with each of the optical signals, one ormore other factors, or any combination thereof. For example, opticalsignals having a lower latency and/or a higher pre-FEC Q may be selectedover optical signals having a higher latency and/or a lower pre-FEC Q.In some implementations, the hub nodes 104 a and 104 b can exchange thedata that they receive from the leaf nodes, such that each hub node 104a and 104 b has a record of the data.

FIG. 9 shows an example configuration of the hub nodes 104 a and 104 bfor receiving data to be transmitted to the leaf nodes 106 a-106 p andreceiving data from the leaf nodes 106 a-106 p (e.g., as described withrespect to FIG. 8 ).

During an example data transmission operation of the hub nodes 104 a and104 b, a Serializer/Deserializer (SerDes) 902 receives data optical dataD1 to D16 (intended for the leaf nodes 106 a-106 p, respectively). Thedata D1 to D8 is transmitted from the SerDes 902 to a Tx processor 904 aof the first hub node 104 a, and to a Tx processor 904 b of the secondhub node 104 b. In general, the Tx processors 904 a and 904 b can besimilar to the Tx processor 450 shown in FIG. 4A. The Tx processor 904 agenerates a first optical signal including the data D1-D16 modulatedaccording to each of the optical subcarriers SC1-1 to SC16-1 andprovides it a WSS 906 a. The Tx processor 904 b generates a secondoptical signal including the data D1-D16 modulated according to each ofthe optical subcarriers SC1-2 to SC16-2 and provides it a WSS 906 b.

The WSS 906 a selects wavelengths of the modulated optical signalcorresponding to a subset of the optical subcarriers (e.g., the opticalsubcarriers SC1-1-SC16-1), and injects the selected wavelengths of themodulated optical signal into the first optical signal path 108 a (e.g.,the “hub working Tx” path). The other WSS 906 b selects wavelengths ofthe modulated optical signal corresponding to the other subset of theoptical subcarriers (e.g., the optical subcarriers SC1-2-SC16-2), andinjects the selected wavelengths of the modulated optical signal intothe second optical signal path 108 b (e.g., the “hub protect Tx” path).

During an example data receipt operation of the hub nodes 104 a and 104b, a WSS 906 c receives a first optical signal from the first opticalpath 108 a (e.g., the “hub protect Rx” path), and a WSS 906 d receives asecond optical signal from the second optical path 108 b (e.g., the “hubworking Tx” path). The first optical signal can include, for example, afirst instance of data D1′-D16′ transmitted by the leaf nodes 106 a-106p, respectively. Further, the second optical signal can include a secondinstance of the data D1′-D16′ transmitted by the leaf nodes 106 a-106 p,respectively. The WSS 416 c selects wavelengths of the first opticalsignal corresponding to a subset of the optical subcarriers (e.g., theoptical subcarriers SC1′-2-SC16′-2), and provides the selectedwavelengths to Rx processor 908 b. Further, the WSS 416 d selectswavelengths of the second optical signal corresponding to a subset ofthe optical subcarriers (e.g., the optical subcarriers SC1′-1-SC16′-1),and provides the selected wavelengths to Rx processor 908 a. In general,the Rx processors 908 a and 908 b can be similar to the Rx processor 452shown in FIG. 4A.

The Rx processors 908 a and 908 b demodulate the selected wavelengths oflight to retrieve respective instances of the data D1′-D16′, andprovides the instances of the data D1′-D16′ to a selection module 910.For each of the data D1′-D16′, the selection module 910 can select theinstance of the data provided by one of the Rx processors over theother. For example, as described above, if the selection module 910 onlyreceives a single instance of data from a particular leaf node (e.g.,due to a fiber cut in the access ring 102), the selection module 910 canselect that instance of data and output it for further processing (e.g.,via an output port 912). Further, as described above, if the selectionmodule 910 receives multiple instances of data from a particular leafnode, the selection module 910 can select one of the instances of databased on one more section factors, and output the selected instance ofdata for further processing (e.g., via an output port 912). For example,as described above, optical signals can be selected based on a measuredor estimated latency associated with each of the optical signalsreceived by the hub nodes 104 a and 104 b, a pre-FEC Q associated witheach of the optical signals, one or more other factors, or anycombination thereof.

Examples of data allocation and subcarrier transmission are describednext with reference to FIGS. 10 and 11A-11C.

FIG. 10 illustrates an example transmitter 1000 than can be included ina network node (e.g., one or more of the hub nodes 104, 104 a, and 104b, or leaf nodes 106 a-106 n described above). The transmitter 1000includes several inputs 1050 (e.g., to receiving respective data D1-D8),as well as a transmitter DSP (Tx DSP) 1002 and a D/A and optics block1001. In this example, 8 inputs 1050 are shown, although more or fewerinputs may be provided than that shown in FIG. 10 .

Based on the signal received from the inputs 1050, the DSP 1002 maysupply several outputs to D/A and optics block 1001 includingoptical-to-analog conversion (DAC) circuits 1004 a 1004 d (which may bereferred to collectively as DACs 1004), which convert optical signalreceived from the DSP 1002 into corresponding analog signals. The D/Aand optics block 1001 also includes driver circuits 1006 a to 1006 d(which may be referred to collectively as driver circuits 1006) thatreceive the analog signals from the DACs 1004 a to 1004 d and adjust thevoltages or other characteristics thereof to provide drive signals to acorresponding one of the modulators 1010 a to 1010 d.

The D/A and optics block 1001 further includes modulators 1010 a to 1010d (which may be referred to collectively as modulators 1010 or opticalmodulators 1010), each of which may be, for example, a Mach-Zehndermodulator (MZM) that modulates the phase and/or amplitude of the lightoutput from a laser 1008. As further shown in FIG. 10 , light outputfrom the laser 1008, also included in the block 1001, is split such thata first portion of the light is supplied to a first MZM pairing,including MZMs 1010 a and 1010 b, and a second portion of the light issupplied to a second MZM pairing, including MZMs 1010 c and 1010 d. Thefirst portion of the light is split further into third and fourthportions, such that the third portion is modulated by MZM 1010 a toprovide an in-phase (I) component of an X (or TE) polarization componentof a modulated optical signal, and the fourth portion is modulated byMZM 1010 b and fed to phase shifter 1012 a to shift the phase of suchlight by 90 degrees in order to provide a quadrature (Q) component ofthe X polarization component of the modulated optical signal. Similarly,the second portion of the light is further split into fifth and sixthportions, such that the fifth portion is modulated by MZM 1010 c toprovide an I component of a Y (or TM) polarization component of themodulated optical signal, and the sixth portion is modulated by MZM 1010d and fed to phase shifter 1012 b to shift the phase of such light by 90degrees to provide a Q component of the Y polarization component of themodulated optical signal.

The optical outputs of the MZMs 1010 a and 1010 b are combined toprovide an X polarized optical signal including I and Q components andare fed to a polarization beam combiner (PBC) 1014 provided in the block1001. In addition, the outputs of the MZMs 1010 c and 1010 d arecombined to provide an optical signal that is fed to a polarizationrotator 1013, further provided in the block 1001, that rotates thepolarization of such optical signal to provide a modulated opticalsignal having a Y (or TM) polarization. The Y polarized modulatedoptical signal also is provided to the PBC 1014, which combines the Xand Y polarized modulated optical signals to provide a polarizationmultiplexed (“dual-pol”) modulated optical signal onto optical fiber1016, for example, which may be included as a segment of optical fiberin the optical paths 108 a and/or 108 b.

The polarization multiplexed optical signal output from D/A and opticsblock 1001 includes subcarriers SC1-SC8 noted above, such that eachsubcarrier has X and Y polarization components and I and Q components.Moreover, each subcarrier SC1 to SC8 may be associated with orcorresponds to a respective one of the inputs 1150.

In some implementations, the DSP 1002 can be similar to the DSP 450shown in FIG. 4A.

FIG. 11A shows an example of DSP 1002 in greater detail. The DSP 1002can include splitters 1160 a to 1160 h (which may be referred tocollectively as splitters 1160). Each of the splitters 1160 a to 1160 hreceives a respective one of the inputs 1050 (e.g., one of data D1-D8),splits the received input into two signals, and provides each of thesignals to a respective one of FEC encoders 1102 a to 1002 p (which maybe referred to collectively as FEC encoders 1102). FEC encoders 1102 ato 1102 p carry out forward error correction coding on a correspondingone of the signals, such as, by adding parity bits to the received data.The FEC encoders 1102 a to 1102 p may also provide timing skew betweenthe subcarriers to correct for skew induced by link between networknodes (e.g., one or more of the hub nodes 104, 104 a, and 104 b, or leafnodes 106 a-106 n described above). In addition, the FEC encoders 1102 ato 1102 p may interleave the received data.

Each of the FEC encoders 1102 a-1102 p provides an output to acorresponding one of a plurality of bits-to-symbol circuits, 1104 a-1104p. Each of the bits-to-symbol circuits 1104 a-1104 p (which may bereferred to collectively as bits-to-symbol circuits 1104) may map theencoded bits to symbols on a complex plane. For example, bits-to-symbolcircuits 1104 a-1104 p may map four bits to a symbol in adual-polarization QPSK constellation. Each of bits-to-symbol circuits1104 a-1104 p provides first symbols, having the complex representationXI+j*XQ, associated with a respective one of the inputs 1150, such asD1, to DSP portion 1103. Data indicative of such first symbols iscarried by the X polarization component of each subcarrier SC-1-SC-16.

Each of bits-to-symbol circuits 1104 a-1104 p further can provide secondsymbols having the complex representation YI+j*YQ, also associated witha corresponding output of outputs. Data indicative of such secondsymbols, however, is carried by the Y polarization component of each ofsubcarriers SC-1 to SC-16.

Such mapping, as carried by about circuit 1104 a to 1004 p define, inone example, a particular modulation format for each subcarrier. Thatis, such circuit may define a mapping for all the optical subcarrierthat is indicative of a binary phase shift keying (BPSK) modulationformat, a quadrature phase shift keying (QPSK) modulation format, or anm-quadrature amplitude modulation (QAM, where m is a positive integer,e.g., 4, 8, 16, or 64) format. In another example, one or more of theoptical subcarriers may have a modulation format that is different thanthe modulation format of other optical subcarriers. That is, one of theoptical subcarriers have a QPSK modulation format and another opticalsubcarrier has a different modulation format, such as 8-QAM or 16-QAM.In another example, one of the optical subcarriers has an 8-QAMmodulation format and another optical subcarrier has a 16 QAM modulationformat. Accordingly, although all the optical subcarriers may carry dataat the same data and or baud rate, consistent with an aspect of thepresent disclosure one or more of the optical subcarriers may carry dataat a different data or baud rate than one or more of the other opticalsubcarriers. Moreover, modulation formats, baud rates and data rates maybe changed over time depending on capacity requirements, for example.Adjusting such parameters may be achieved, for example, by applyingappropriate signals to mappers 1104 based on control information or datadescribed herein and the communication of such data as further disclosedherein between hub and leaf nodes.

As further shown in FIG. 11A, each of the first symbols output from eachof bits-to-symbol circuits 1104 a-1104 p is supplied to a respective oneof first overlap and save buffers 1105 a-1105 p (which may be referredto collectively as overlap and save buffers 1105) that may buffer 256symbols, for example. Each of the overlap and save buffers 1105 a-1105 pmay receive 128 of the first symbols or another number of such symbolsat a time from a corresponding one of bits to symbol circuits 1104a-1104 p. Thus, overlap and save buffers 1105 a-1105 p may combine 128new symbols from bits to symbol circuits 1104 a-1104 p, with theprevious 128 symbols received from bits to symbol circuits 1104 a-1104p.

Each overlap and save buffer 1105 a-1105 p supplies an output, which isin the time domain, to a corresponding one of fast Fourier Transform(FFT) circuits 1106 a-1106 p (which may be referred to collectively asFFT circuits 1106). In one example, the output includes 256 symbols oranother number of symbols. Each of the FFTs 1106 a-1106 p converts thereceived symbols to the frequency domain using or based on, for example,a fast Fourier transform. Each of the FFTs 1106 a-1106 p can provide thefrequency domain data to bins and switches blocks 1121 a-1121 p (whichmay be referred to collectively as bins and switches blocks 1121). Asdiscussed in greater detail below, bins and switches blocks 1121 a-1121p can include, for example, memories or registers, also referred to asfrequency bins (FB) or points, that store frequency componentsassociated with each subcarrier SC.

Selected frequency bins FB are shown in FIG. 11B. In someimplementations, the frequency bins FB can be included, for example, ina DSP (e.g., the DSP 1002 described with respect to FIG. 11A). Groups ofsuch frequency bins FB are associated with given subcarriers.Accordingly, for example, a first group of frequency bins, FB1-1 toFB1-n is associated with SC1 and a second group of frequency bins FB16-1to FB16-n with SC16 (where n is a positive integer). As further shown inFIG. 11B, each of frequency bins FB is further coupled to a respectiveone of the outputs from switches SW1-1′ to SW1-n′ and SW16-1′ toSW16-n′.

Each of the inputs 1050 selectively supplies either frequency domaindata output from one of FFT circuits 1106 a to 1106 p or a predeterminedvalue, such as 0. In order to block or eliminate transmission of aparticular subcarrier, the outputs from switches SW that associated withthe group of frequency bins FB that associated with that subcarrier areconfigured to supply the zero value to corresponding frequency bins.Accordingly, for example, in order to block subcarrier SC1, switchesSW1-1′ to SW1-n′ supply zero (0) values to a respective one of frequencybins FB1-1 to FB1-n. Further processing, as described below, of the zero(0) values by replicator components 1107 as well as other components andcircuits in DSP 1002 result in drive signals supplied to modulators1010, such that subcarrier SC1 is omitted from the optical output fromthe modulators.

On the other hand, switches SW′ may be configured to supply the outputsof FFTs 1106 a-1106 p (e.g., frequency domain data FD), to correspondingfrequency bins FB. Further processing of the contents of frequency binsFB by replicator components 1107 and other circuits in DSP 1002 resultin drive signals supplied to modulators 1010, whereby, based on suchdrive signals, optical subcarriers are generated that correspond to thefrequency bin groupings associated with that subcarrier.

In the example discussed above, the switches SW1-1′ to SW1-n′ supplyfrequency domain data FD1-1 to FD-n from FFT 1106 a to a respective oneof the switches SW1-1 to SW1-n. These switches, in turn, supply thefrequency domain data to a respective one of the frequency bins FB1-1 toFB1-n for further processing, as described in greater detail below.

Each of the replicator components or circuits 1107 a to 1007 p (whichmay be referred to collectively as replicator components or circuits1107) can replicate the contents of the frequency bins FB and store suchcontents (e.g., for T/2 based filtering of the subcarrier) in arespective one of the plurality of replicator components. Suchreplication can increase the sample rate. In addition, the replicatorcomponents or circuits 1107 a-1007 p may arrange or align the contentsof the frequency bins to fall within the bandwidths associated with thepulse shaped filter circuits 1108 a to 1108 p described below.

Each of the pulse shape filter circuits 1108 a to 1108 p (which may bereferred to collectively as pulse shape filter circuits 1108) can applya pulse shaping filter to the data stored in the 512 frequency bins of arespective one of the replicator components or circuits 1107 a-1107 p tothereby provide a respective one of a plurality of filtered outputs,which are multiplexed and subject to an inverse FFT, as described below.The pulse shape filter circuits 1108 a-1108 p calculate the transitionsbetween the symbols and the desired subcarrier spectrum so that thesubcarriers can be packed together spectrally for transmission, e.g.,with a close frequency separation. The pulse shape filter circuits 1108a-1108 p also may be used to introduce timing skew between thesubcarriers to correct for timing skew induced by links between networknodes (e.g., one or more of the hub nodes 104, 104 a, and 104 b, or leafnodes 106 a-106 n described above). The multiplexer component 1109,which may include a multiplexer circuit or memory, can receive thefiltered outputs from pulse shape filter circuits 1108 a to 1108 p, andmultiplex or combine such outputs together to form an element vector.

Next, the IFFT circuit or component 1110 a can receive the elementvector and provide a corresponding time domain signal or data based onan inverse fast Fourier transform (IFFT). In one example, the timedomain signal may have a rate of 64 GSample/s. A take last buffer ormemory circuit 1111 a, for example, can select the last 1024 samples, oranother number of samples, from an output of the IFFT component orcircuit 1110 a and supply the samples to DACs 1004 a and 1004 b (seeFIG. 10 ) at 64 GSample/s, for example. As noted above, the DAC 1004 ais associated with the in-phase (I) component of the X pol signal, andthe DAC 1004 b is associated with the quadrature (Q) component of the Ypol signal. Accordingly, consistent with the complex representationXI+jXQ, the DAC 1004 a receives values associated with XI and the DAC1004 b receives values associated with jXQ. As indicated by FIG. 10 ,based on these inputs, the DACs 1004 a and 1004 b provide analog outputsto the MZMD 1006 a and the MZMD 1006 b, respectively, as discussedabove.

As further shown in FIG. 11A, each of bits-to-symbol circuits 1104 a to1104 p outputs a corresponding one of symbols indicative of data carriedby the Y polarization component of the polarization multiplexedmodulated optical signal output on fiber 1016. As further noted above,these symbols may have the complex representation YI+j*YQ. Each suchsymbol may be processed by a respective one of overlap and save buffers1115 a-1115 p (which may be referred to collectively as overlap and savebuffers 1115), a respective one of the FFT circuits 1116 a-1016 p (whichmay be referred to collectively as FFT circuits 1116), a respective oneof the replicator components or circuits 1117 a-1117 p (which may bereferred to collectively as replicator components or circuits 1117), thepulse shape filter circuits 1118 a-1118 p (which may be referred tocollectively as pulse shape filter circuits 1118), the multiplexer ormemory 1119, the IFFT 1110 b, and the take last buffer or memory circuit1111 b, to provide processed symbols having the representation YI+j*YQin a manner similar to or the same as that discussed above in generatingprocessed symbols XI+j*XQ output from the take last circuit 1111 a. Inaddition, symbol components YI and YQ are provided to the DACs 1004 cand 1004 d (FIG. 10 ), respectively. Based on these inputs, the DACs1004 c and 1004 d provide analog outputs to the MZMD 1006 c and the MZMD1006 d, respectively, as discussed above.

While FIG. 11A shows the DSP 1002 as including a particular number andarrangement of functional components, in some implementations, the DSP1002 may include additional functional components, fewer functionalcomponents, different functional components, or differently arrangedfunctional components. In addition, typically the number of overlap andsave buffers, FFTs, replicator circuits, and pulse shape filtersassociated with the X component may be equal to the number of switchoutputs, and the number of such circuits associated with the Y componentmay also be equal to the number of switch outputs. However, in otherexamples, the number of switch outputs may be different from the numberof these circuits.

As noted above, based on the outputs of the MZMDs 1006 a to 1006 d, aplurality of optical subcarriers SC1 to SC16 may be output onto theoptical fiber 1016 (FIG. 10 ).

Consistent with an aspect of the present disclosure, the number ofsubcarriers transmitted by the network nodes (e.g., the hub nodes 104,104 a, and 104 b and/or leaf nodes 106 a-106 n described above) can varyover time based, for example, on capacity requirements at the networknodes. For example, if less downstream capacity is required initially atone or more of the network nodes, a transmitter may be may be configuredto output fewer optical subcarriers. On the other hand, if furthercapacity is required later, a transmitter may provide more opticalsubcarriers.

In addition, if based on changing capacity requirements, a particularnetwork node needs to be adjusted, for example, the output capacity ofsuch network node may be increased or decreased by, in a correspondingmanner, increasing or decreasing the number of optical subcarriersoutput from the network node.

As noted above, by storing and subsequently processing zeros (0s) orother predetermined values in frequency bin FB groupings associated witha given subcarrier SC, that subcarrier may be removed or eliminated. Toadd or reinstate such subcarrier, frequency domain data output from theFFTs 1106 a-1106 p may be stored in frequency bins FB and subsequentlyprocessed to provide the corresponding subcarrier. Thus, subcarriers maybe selectively added or removed from the optical outputs of thetransmitters of network nodes, such that the number of subcarriersoutput from such transmitters may be varied, as desired.

In the above example, zeros (0s) or other predetermined values arestored in selected frequency bins FBs to prevent transmission of aparticular subcarrier SC. Such zeroes or values may, instead, beprovided, for example, in a manner similar to that described above, atthe outputs of corresponding replicator components 1107 a-1107 p orstored in corresponding locations in memory or multiplexer 1109.Alternatively, the zeroes or values noted above may be provided, forexample, in a manner similar to that described above, at correspondingoutputs of pulse shape filters 1108 a-1108 p.

In a further example, a corresponding one of the pulse shape filters 110a to 1108 p may selectively generate zeroes or predetermined valuesthat, when further processed, also cause one or more subcarriers SC tobe omitted from the output of the transmitter of a network node. Inparticular, as shown in FIG. 11C, pulse shape filters 1108 a-1108 p areshown as including groups of multiplier circuits M1-1 to M1-n M16-1 toM16-n (also individually or collectively referred to as M). In someimplementations, the pulse shape filters 1108 a-1108 p can be included,for example, in a DSP (e.g., the DSP 1002 described with respect to FIG.11A). Each multiplier circuit M constitutes part of a correspondingbutterfly filter. In addition, each multiplier circuit grouping isassociated with a corresponding one of subcarriers SC.

Each multiplier circuit M receives a corresponding one of outputgroupings RD1-1 to RD1-n RD16-1 to RD16-n from replicator components1107 a-1107 p. In order to remove or eliminate one of subcarriers SC,multiplier circuits M receiving the outputs within a particular groupingassociated with that subcarrier multiply such outputs by zero (0), suchthat each multiplier M within that group generates a product equal tozero (0). The zero products then are subject to further processingsimilar to that described above to provide drive signals to themodulators 1010 that result in a corresponding subcarrier SC beingomitted from the output of a transmitter.

On the other hand, in order to provide a subcarrier SC, each of themultiplier circuits M within a particular groping may multiply acorresponding one of replicator outputs RD by a respective one ofcoefficients C1-1 to C1-n C16-1 to C16-n, which results in at least somenon-zero products being output. Based on the products output from thecorresponding multiplier grouping, drive signals are provided to themodulators 1010 to output the desired subcarrier SC from a transmitter.

Accordingly, for example, in order to block or eliminate subcarrier SC1,each of multiplier circuits M1-1 to M1-n (associated with subcarrierSC1) multiplies a respective one of replicator outputs RD1-1 to RD1-n byzero (0). Each such multiplier circuit, therefore, provides a productequal to zero, which is further processed, as noted above, such thatresulting drive signals cause modulators 1010 to provide an opticaloutput without SC1. In order to reinstate SC1, multiplier circuits M1-1to M1-n multiply a corresponding one of appropriate coefficients C1-1 toC1-n by a respective one of replicator outputs RD1-1 to RD1-n to provideproducts, at least some of which are non-zero. Based on these products,as noted above, modulator drive signals are generated that result insubcarrier SC1 being output.

The above examples are described in connection with generating orremoving the X component of a subcarrier SC. The processes and circuitrydescribed above is employed or included in DSP 1002 and opticalcircuitry used to generate the Y component of the subcarrier to beblocked. For example, switches and bins circuit blocks 1122 a-1122 p,have a similar structure and operate in a similar manner as switches andbins circuit blocks 1121 described above to provide zeroes or frequencydomain data as the case may be to selectively block the Y component ofone or more subcarriers SC. Alternatively, multiplier circuits, likethose described above in connection with FIG. 11C may be provided tosupply zero products output from selected pulse shape filters 1118 inorder to block the Y component of a particular subcarrier or, ifnon-zero coefficients are provided to the multiplier circuits instead,generate the subcarrier.

Optical subcarriers SC1 to SC16 may be provided to network nodes, suchas the leaf nodes 106 a-106 h, as described above. An example ofreceiver circuit of one of a network node will be described next withreference to FIG. 12 .

As shown in FIG. 12 , an optical receiver may include an Rx optics andA/D block 1200, which, in conjunction with DSP 1250, may carry outcoherent detection. Block 1200 may include a polarization splitter (PBS)1205 with first (1205 a) and second (1105 b) outputs), a localoscillator (LO) laser 1210, 90 degree optical hybrids or mixers 1220 aand 1220 b, detectors 1230 a and 1230 b (each including either a singlephotodiode or balanced photodiode), AC coupling capacitors 1232 a and1232 b, transimpedance amplifiers/automatic gain control circuitsTIA/AGC 1234 a and 1234 b, ADCs 1240 a and 1240 b.

Polarization beam splitter (PBS) 1205 may include a polarizationsplitter that receives an input polarization multiplexed optical signalincluding optical subcarriers SC1 to SC16 supplied by optical fiber link1201, which may be, for example, an optical fiber segment as part of oneof optical paths 108 a and 108 b described above. The PBS 1205 may splitthe incoming optical signal into the two X and Y orthogonal polarizationcomponents. The Y component may be supplied to a polarization rotator1206 that rotates the polarization of the Y component to have the Xpolarization. Hybrid mixers 1220 may combine the X and rotated Ypolarization components with light from local oscillator laser 1210,which, in one example, is a tunable laser. For example, hybrid mixer1220 a may combine a first polarization signal (e.g., the component ofthe incoming optical signal having a first or X (TE) polarization outputfrom a first PBS port with light from local oscillator 1210, and hybridmixer 1220 b may combine the rotated polarization signal (e.g., thecomponent of the incoming optical signal having a second or Y (TM)polarization output from a second PBS port) with the light from localoscillator 1210. In one example, polarization rotator 1206 may beprovided at the PBS output to rotate Y component polarization to havethe X polarization.

Detectors 1230 may detect mixing products output from the opticalhybrids, to form corresponding voltage signals, which are subject to ACcoupling by capacitors 1232 a and 1232 b as well as amplification andgain control by TIA/AGCs 1234 a and 1234 b. The outputs of TIA/AGCs 1234a and 1234 b and ADCs 1240 may convert the voltage signals to opticalsamples. For example, two detectors (e.g., photodiodes) 1230 a maydetect the X polarization signals to form the corresponding voltagesignals, and a corresponding two ADCs 1240 a may convert the voltagesignals to optical samples for the first polarization signals afteramplification, gain control and AC coupling. Similarly, two detectors1230 b may detect the rotated Y polarization signals to form thecorresponding voltage signals, and a corresponding two ADCs 1240 b mayconvert the voltage signals to optical samples for the secondpolarization signals after amplification, gain control and AC coupling.RX DSP 1250 may process the optical samples associated with the X and Ypolarization components to output data associated with one or moresubcarriers within a group of subcarriers SC1 to SC16 encompassed by thebandwidth associated with the secondary node housing the particular DSP1250.

While FIG. 12 shows an optical receiver as including a particular numberand arrangement of components, in some implementations, an opticalreceiver may include additional components, fewer components, differentcomponents, or differently arranged components. The number of detectors1230 and/or ADCs 1240 may be selected to implement an optical receiverthat is capable of receiving a polarization multiplexed signal. In someinstances, one of the components illustrated in FIG. 12 can carry out afunction described herein as being carry out by another one of thecomponents illustrated in FIG. 12 .

Consistent with the present disclosure, in order to select a particularsubcarrier or group of subcarriers at a network node, the localoscillator 1210 may be tuned to output light having a wavelength orfrequency relatively close to the selected subcarrier wavelength(s) tothereby cause a beating between the local oscillator light and theselected subcarrier(s). Such beating will either not occur or will besignificantly attenuated for the other non-selected subcarriers so thatdata carried by the selected subcarrier(s) is detected and processed bythe DSP 1250.

In some implementations, certain subcarriers SC may be detected bymultiple leaf nodes. If the data associated with such subcarriers SC isintended for one of those leaf nodes, but not the other, switchcircuitry, as noted above, may be provided in the leaf nodes to outputthe data selectively at the intended secondary node but not the others.For example, as further shown in FIG. 12 , an output 1290 can beprovided at the output of DSP 1250 to selectively output the datadetected from the received subcarriers (e.g., one of D1-D8). Forexample, if the Rx optics and A/D block 1200 and the DSP 1250 shown inFIG. 12 is implemented in the leaf node 106 b shown in FIGS. 2A and 2B,the DSP 1250 can output the data D2 via the output 1290.

FIG. 13 illustrates exemplary components of receiver optical signalprocessor (DSP) 1250. As noted above, analog-to-optical (A/D) circuits1240 a and 1240 b (FIG. 12 ) output optical samples corresponding to theanalog inputs supplied thereto. In one example, the samples may besupplied by each A/D circuit at a rate of 64 GSamples/s. The opticalsamples correspond to symbols carried by the X polarization of theoptical subcarriers and may be represented by the complex number XI+jXQ.The optical samples may be provided to overlap and save buffer 1305 a,as shown in FIG. 13 . FFT component or circuit 1310 a may receive the2048 vector elements, for example, from the overlap and save buffer 1305a and convert the vector elements to the frequency domain using, forexample, a fast Fourier transform (FFT). The FFT component 1310 a mayconvert the 2048 vector elements to 2048 frequency components, each ofwhich may be stored in a register or “bin” or other memory, as a resultof carrying out the FFT.

The frequency components then may be demultiplexed by demultiplexer 1311a, and groups of such components may be supplied to a respective one ofchromatic dispersion equalizer circuits CDEQ 1312 a,1 to 1312 a,16, eachof which may include a finite impulse response (FIR) filter thatcorrects, offsets or reduces the effects of, or errors associated with,chromatic dispersion of the transmitted optical subcarriers. Each ofCDEQ circuits 1312 a,1 to 1312 a,16 supplies an output to acorresponding polarization mode dispersion (PMD) equalizer circuit 1325a to 1325 p (which individually or collectively may be referred to as1225).

Optical samples output from A/D circuits 1340 b associated with Ypolarization components of subcarrier SC1 may be processed in a similarmanner to that of optical samples output from A/D circuits 1340 a andassociated with the X polarization component of each subcarrier. Namely,overlap and save buffer 1305 b, FFT 1310 b, demultiplexer 1311 b, andCDEQ circuits 1312 b,1 to 1312 b,16 may have a similar structure andoperate in a similar fashion as buffer 1305 a, FFT 1310 a, demultiplexer1322 a, and CDEQ circuits 1312 a,1 to 1312 a,16, respectively. Forexample, each of CDEQ circuits 1312 b,1 to 1312 b,16 may include an FIRfilter that corrects, offsets, or reduces the effects of, or errorsassociated with, chromatic dispersion of the transmitted opticalsubcarriers. In addition, each of CDEQ circuits 1312 b,1 to 1312 b,16provide an output to a corresponding one of PMDEQ 1325 a to 1325 p.

As further shown in FIG. 13 the output of one of the CDEQ circuits, suchas CDEQ 1312 a,1 can be supplied to clock phase detector circuit 1313 todetermine a clock phase or clock timing associated with the receivedsubcarriers. Such phase or timing information or data may be supplied toADCs 1240 a and 1240 b to adjust or control the timing of the opticalsamples output from ADCs 1240 a and 1240 b.

Each of PMDEQ circuits 1325 may include another FIR filter thatcorrects, offsets or reduces the effects of, or errors associated with,PMD of the transmitted optical subcarriers. Each of PMDEQ circuits 1325may supply a first output to a respective one of IFFT components orcircuits 1330 a,1 to 1330 p,1 and a second output to a respective one ofIFFT components or circuits 1330 a,2 to 1330 p,2, each of which mayconvert a 256-element vector, in this example, back to the time domainas 256 samples in accordance with, for example, an inverse fast Fouriertransform (IFFT).

Time domain signals or data output from IFFT 1330 a,1 to 1330 p,1 aresupplied to a corresponding one of Xpol carrier phase correctioncircuits 1340 a,1 to 1340 p,1, which may apply carrier recoverytechniques to compensate for X polarization transmitter (e.g., laser1008) and receiver (e.g., local oscillator laser 1210) linewidths. Insome implementations, each carrier phase correction circuit 1340 a,1 to1340 p,1 may compensate or correct for frequency and/or phasedifferences between the X polarization of the transmit signal and the Xpolarization of light from the local oscillator 1200 based on an outputof Xpol carrier recovery circuit 1340 a,1, which performs carrierrecovery in connection with one of the subcarrier based on the outputsof IFFT 1330 a,1. After such X polarization carrier phase correction,the data associated with the X polarization component may be representedas symbols having the complex representation xi+j*xq in a constellation,such as a QPSK constellation or a constellation associated with anothermodulation formation, such as an m-quadrature amplitude modulation(QAM), m being an integer. In some implementations, the taps of the FIRfilter included in one or more of PMDEQ circuits 1325 may be updatedbased on the output of at least one of carrier phase correction circuits1340 a,1 to 1340 p,1.

In a similar manner, time domain signals or data output from IFFT 1330a,2 to 1330 p,2 are supplied to a corresponding one of Ypol carrierphase correction circuits 1340 a,2 to 1340 p,2, which may compensate orcorrect for Y polarization transmitter (e.g., laser 1008) and receiver(e.g., local oscillator laser 1210) linewidths. In some implementations,each carrier phase correction circuit 1340 a,2 to 1340 p,2 also maycorrect or compensate for frequency and/or phase differences between theY polarization of the transmit signal and the Y polarization of lightfrom the local oscillator 1210. After such Y polarization carrier phasecorrection, the data associated with the Y polarization component may berepresented as symbols having the complex representation yi+j*yq in aconstellation, such as a QPSK constellation or a constellationassociated with another modulation formation, such as an m-quadratureamplitude modulation (QAM), m being an integer. In some implementations,the output of one of circuits 1340 a,2 to 1340 p,2 may be used to updatethe taps of the FIR filter included in one or more of PMDEQ circuits1325 instead of, or in addition to, the output of at least one of thecarrier recovery circuits 1340 a,1 to 1340 p,1.

As further shown in FIG. 13 , the output of carrier recovery circuits,e.g., carrier recovery circuit 1340 a,1, also may be supplied to carrierphase correction circuits 1340 a,1 to 1340 p,1 and 1340 a,2 to 1340 p,2,whereby the phase correction circuits may determine or calculate acorrected carrier phase associated with each of the received subcarriersbased on one of the recovered carriers, instead of providing multiplecarrier recovery circuits, each of which is associated with acorresponding subcarrier. The equalizer, carrier recovery, and clockrecovery may be further enhanced by utilizing the known (training) bitsthat may be included in control signals CNT, for example by providing anabsolute phase reference between the transmitted and local oscillatorlasers.

Each of the symbols-to-bits circuits or components 1345 a,1 to 1345 p,1may receive the symbols output from a corresponding one of circuits 1340a,1 to 1340 p,1 and map the symbols back to bits. For example, each ofthe symbol-to-bits components 1345 a,1 to 1345 p,1 may map one Xpolarization symbol, in a QPSK or m-QAM constellation, to Z bits, whereZ is an integer. For dual-polarization QPSK modulated subcarriers, Z isfour. Bits output from each of component 1345 a,1 to 1345 p,1 areprovided to a corresponding one of FEC decoder circuits 1360 a to 1360p.

Y polarization symbols are output form a respective one of circuits 134a,2 to 1340 p,2, each of which has the complex representation yi+j*yqassociated with data carried by the Y polarization component. Each Ypolarization, like the X polarization symbols noted above, may beprovided to a corresponding one of bit-to-symbol circuits or components1345 a,2 to 1345 h,2, each of which has a similar structure and operatesin a similar manner as symbols-to-bits component 1345 a,1 to 1345 h,1.Each of circuits 1345 a,2 to 1345 p,2 may provide an output to acorresponding one of FEC decoder circuits 1360 a to 1360 p.

Each of FEC decoder circuits 1360 may remove errors in the outputs ofsymbol-to-bit circuits 1345 using, for example, forward errorcorrection. Such error corrected bits, which may include user data foroutput from a leaf node, may be supplied to a corresponding one ofswitch circuits SW-0 to SW-8. As noted above, switch circuits SW-0 toSW-16 (e.g., as shown in FIG. 11B) in each leaf node may selectivelysupply or block data based on whether such data is intended to be outputfrom the secondary node.

Consistent with another aspect of the present disclosure, data may beblocked from output from DSP 1250 without the use of switches SW-0 toSW-16. In one example similar to an example described above, zero (0) orother predetermined values may be stored in frequency bins associatedwith the blocked data, as well as the subcarrier corresponding to theblocked data. Further processing described above of such zeroes orpredetermined data by circuitry in DSP 1250 will result in null or zerodata outputs, for example, from a corresponding one of FEC decoders1260. Switch circuits provided at the outputs of FFTs 1310 a and 1310 b,like switch circuits SW described above in FIG. 11B, may be provided toselectively insert zeroes or predetermined values for selectivelyblocking corresponding output data from DSP 1250. Such switches also maybe provided at the output of or within demultiplexers 1311 a and 1311 bto selectively supply zero or predetermined values.

In another example, zeroes (0s) may be inserted in chromatic dispersionequalizer (CDEQ) circuits 1312 associated with both the X and Ypolarization components of each subcarrier. In particular, multipliercircuits (provided in corresponding butterfly filter circuits), likemultiplier circuits M described above, may selectively multiply theinputs to the CDEQ circuit 1312 by either zero or a desired coefficient.As discussed above in connection with FIG. 11C, multiplication by a zerogenerates a zero product. When such zero products are further processedby corresponding circuitry in DSP 1250, e.g., corresponding IFFTs 1330,carrier phase correction components 1340, symbol-to-bits components1345, and FEC decoder, a corresponding output of DSP 1250 will also bezero. Accordingly, data associated with a subcarrier SC received by aleaf node, but not intended for output from that leaf node, can beblocked.

If, on the other hand, capacity requirements change and such previouslyblocked data is to be output from a given leaf node receiver DSP 1250,appropriately coefficients may be supplied to the multiplier circuits,such that at least some of the inputs thereto are not multiplied byzero. Upon further processing, as noted above, data associated with theinputs to the multiplier circuits and corresponding to a particularsubcarrier SC is output from leaf node receiver DSP 1250.

As described above, a node may receive one or more signals that includeinformation indicative of the same data, and select one of the signalsfrom which the retrieve the data. As an example, referring to FIG. 13 ,the output of the DSP 1250 can be selected by selection circuitry 1380from among the outputs of the FEC decoders 1360 a-1360 h. The selectioncircuitry 1380 can select between the outputs of one or more of the FECdecoders 1360 a-1360 h based on one or more criteria. For example, asdescribed above, the selection circuitry 1380 can make a selected basedon criteria such as a measured or estimated latency associated with eachof the optical signals received by the node (e.g., a latency associatedwith transmitting the optical signal to the node from another node), apre-forward error correction quality factor (pre-FEC Q) associated witheach of the optical signals, one or more other factors, or anycombination thereof. For example, the selection circuitry 1380 canselect an instance of the data that was included in an optical signalhaving a lower latency and/or a higher pre-FEC Q over an instance of thedata that was included in an optical signal having a higher latencyand/or a lower pre-FEC Q.

As an example, if the DSP 1250 shown in FIG. 13 is implemented in theleaf node 106 b shown in FIGS. 2A and 2B, the selection circuitry 1380can receive one or more instances of the data D2. The selectioncircuitry 1380 can select between the received instances of the data D2,and output it from the DSP 1250.

While FIG. 13 shows DSP 1250 as including a particular number andarrangement of functional components, in some implementations, DSP 1250may include additional functional components, fewer functionalcomponents, different functional components, or differently arrangedfunctional components.

Upstream transmission from a leaf node to hub node will be describednext with reference to FIGS. 14 and 15 .

FIG. 14 shows an example of leaf node transmitter 1400 in greaterdetail. The transmitter 1400 includes an input 1450 for receiving data(e.g., one of data D1′ to D8′). As an example, if the transmitter 1400is implemented in leaf node 106 b shown in FIGS. 2A and 2B, the input1450 can be configured to receive data D2′. The transmitter 1400 alsoincludes a DSP 1402 and a D/A and optics block 1401.

DSP 1402 may have a similar structure as the Tx processor 508 describedabove with reference to FIGS. 5A, 7A, and 7B, and/or the DSP 1002described above with reference to FIGS. 10 and 11A. In some instances,however, DSP 1402 may have a lower capacity than DSP 1002. For example,the number of circuits, such as FEC encoders, bits-to-symbol mappers,overlap and save buffers, FFT circuits, replicator circuits, and pulseshape filters may be reduced in accordance with the number of inputs toDSP 1402. Accordingly, fewer subcarriers may be output from each of theleaf nodes compared to the number of subcarriers output from hub node.

Based on the data received from the inputs 1450, DSP 1302 may supply aplurality of outputs to D/A and optics block 1401, which may have asimilar construction as D/A and optics block 1001 described above tosupply X and Y polarized optical signals, each including I and Qcomponents, that are combined by a PBC and output onto an optical fibersegment 1416 included in one of optical paths (e.g., optical paths 108 aand 108 b).

Alternatively, based on zeroes (0s) stored or generated in DSP 1402,subcarriers may be blocked or added in a manner similar to thatdescribed above.

FIG. 15 shows an example of hub node receiver 1500 in greater detail.The receiver 1500 includes an input 1550 for receiving optical signals(e.g., from one or more of the 108 a and 108 b). The receiver 1500 alsoincludes an Rx optics and A/D block 1501 and a DSP 1502.

The Rx optics and A/D block 1501 can be similar to the Rx optics and A/Dblock 1200 described above. For example, the Rx optics and A/D block1501 can receive one or more optical signals, and output corresponding Xand Y polarized optical signals, each including I and Q components, tothe DSP 1502

DSP 1502 may have a similar structure as the Rx processor 430 describedabove with reference to FIGS. 4A, 4B, the Rx processors 908 a and 908 bdescribed above with reference to FIG. 9 , and/or the DSP 1250 describedabove with reference to FIGS. 12 and 13 . For example, the DSP 1502 canreceive the optical signals from the Rx optics and A/D block 1501, andoutput data D1′-D8′ transmitted by each of several leaf nodes.

In some instances, DSP 1502 may have a lower capacity than DSP 1250. Forexample, the number of circuits, such as overlap and save buffers, FFTcircuits, demultiplexers, CDEQ circuits, PMDEQ circuits, IFFT circuits,carrier phase correction circuits, symbols-to-bits circuits, and FECdecoders may be reduced in accordance with the number of leaf nodes fromwhich the hub node can receive data. Accordingly, fewer correspondingdata outputs can be provided by the DSP 1502.

In the aforementioned examples, the optical links of a communicationsnetwork 100 are shown and described as unidirectional optical links(e.g., optical signals propagate in a single direction along eachoptical link). However, this need not always be the case. For example,as shown in FIG. 1B, the access ring 102 can be implemented usingseveral bidirectional optical links extending between respective ones ofthe nodes. In these implementations, the first optical path 108 a canrefer to the transmission of data a first direction along the opticallinks of the access ring (e.g., clockwise, in the example shown in FIG.1B), and the second optical path 108 b can refer to the transmission ofdata a second, opposite direction along the same optical links of theaccess ring (e.g., counterclockwise, in the example shown in FIG. 1B).

II. Example Processes for Performing the Techniques Described Herein

FIG. 16A shows an example process 1600 that can be performed using oneor more of the systems described herein. For instance, the 1600 ### canbe performed using an optical communications network 100 and/or one ormore of the components thereof (e.g., as shown in FIGS. 1-15 ).

According to the process 1600, a first network device receives data tobe transmitted to a second network device over an optical communicationsnetwork (block 1602).

In some implementations, the first network device can include one ormore hub network devices, and the second network device can include oneor more leaf network devices, or vice versa. As an example, the firstnetwork device can include the node 104. As another example, the secondnetwork device can include one of the nodes 106 a-106 n.

The first network device transmits first information and secondinformation to the second device (block 1604). The first information isindicative of the data using a first communications link of the opticalcommunications network, and is transmitted using a first subset ofoptical subcarriers. The second information is indicative of the datausing a second communications link of the optical communicationsnetwork, and is transmitted using a second subset of opticalsubcarriers. The first subset of optical subcarriers is different fromthe second subset of optical subcarriers.

In some implementations, the first information and the secondinformation can be identical. In some implementations, the firstinformation can be different from the second information. For example,the first information and the second information can include the samedata modulated according to different digital subcarriers. As anotherexample, the first information and the second information can includethe same data transmitted according to different forward errorcorrection (FEC) schemes (e.g., include different FEC codes or bits).

In some implementations, the first communications link and the secondcommunications link can form at least a portion of a communications ringthat communicatively interconnects the first network device and thesecond network device. As an example, referring to FIG. 1 , the firstcommunications link can include at least a portion of the optical path108 a, and the second communications link can include at least a portionof the optical path 108 b, or vice versa. In some implementations, thefirst communications link can be referred to as a “hub working Tx” path,and the second communications link can be referred to as a “hub protectTx” path, or vice versa.

In some implementations, each of the optical subcarriers in the firstsubset of optical subcarriers and the second subset of opticalsubcarriers can be a respective Nyquist subcarrier. Further, in someimplementations, each of the optical subcarriers are associated withrespective frequencies that do not overlap one another in a frequencydomain.

In some implementations, the first subset of optical subcarriers can beselected from a plurality of optical subcarriers allotted to the firstnetwork device. For example, referring to FIG. 3 , the first networkdevice can be allotted subcarriers S1-SC16 for use in communicating overan optical communications network. The first subset can be selected fromamong the subcarriers SC1-SC16.

In some implementations, the optical subcarriers of the first subset ofoptical subcarriers are associated with respective frequencies that arecontiguous with one another in a frequency domain. As an example,referring to FIG. 3 , the first subset of optical subcarriers can be SC1and SC2.

In some implementations, the second subset of optical subcarriers can beselected from the plurality of optical subcarriers allotted to the firstnetwork device. For example, referring to FIG. 3 , the first networkdevice can be allotted one or more of the subcarriers S1-SC16 for use incommunicating over an optical communications network (e.g., fortransmitting data over the optical communications network). The secondsubset can be selected from among the subcarriers SC1-SC16.

In some implementations, the optical subcarriers of the second subset ofoptical subcarriers can be associated with respective frequencies thatare contiguous with one another in a frequency domain. As an example,referring to FIG. 3 , the second subset of optical subcarriers can beSC9 and SC10.

In some implementations, the first subset of optical subcarriers can beassociated with one or more first frequencies, and the second subset ofoptical subcarriers can be associated with one or more secondfrequencies. In some implementations, the one or more first frequenciesare not contiguous with the one or more second frequencies in afrequency domain. As an example, referring to FIG. 3 , the first subsetof optical subcarriers can be SC1, and the second subset of opticalsubcarriers can be SC9.

In some implementations, the first subset of optical subcarriers can beassociated with one or more first frequencies, and the second subset ofoptical subcarriers can be associated with one or more secondfrequencies. Further, one or more additional optical subcarriers can beassociated with one or more additional frequencies. Further, the one ormore additional frequencies can be disposed between the one or morefirst frequencies and the one or more second frequencies in a frequencydomain. As an example, referring to FIG. 3 , the first subset of opticalsubcarriers can be SC1-SC4, and the second subset of optical subcarrierscan be SC13-SC16, with the additional optical subcarriers SC5-SC12disposed between them in the frequency domain.

In some implementations, the first subset of optical subcarriers can beassociated with one or more first frequencies, and the second subset ofoptical subcarriers can be associated with one or more secondfrequencies. Further, the one or more first frequencies and the one ormore second frequencies can be separated from one another by one or moreadditional frequencies in a frequency domain. As an example, referringto FIG. 3 , a guard band (e.g., a frequency band spanning a range offrequencies) can separate the one or more first frequencies and the oneor more second frequencies from one another.

In some implementations, a number of optical subcarriers in the firstsubset of optical subcarriers can be the same as a number of opticalsubcarriers in the second subset of optical subcarriers. For example,referring to FIG. 3 , the first subset of optical subcarriers can beSC1, and the second subset of optical subcarriers can be SC9.

In some implementations, a number of optical subcarriers in the firstsubset of optical subcarriers can be different from a number of opticalsubcarriers in the second subset of optical subcarriers. For example,referring to FIG. 3 , the first subset of optical subcarriers can be SC1and SC2, and the second subset of optical subcarriers can be SC9.

In some implementations, the first information and the secondinformation can be transmitted by performing one or more particularactions. The actions can include modulating an output of a laser togenerate a modulated optical signal including the first subset ofoptical subcarriers and the second subsets of optical subcarriers,providing the modulated optical signal to an optical splitter, andsplitting the modulated optical signal into a first portion and a secondportion. Each of the first portion and the second portion can includethe first subset of optical subcarriers and the second subset of opticalsubcarriers. Further, the actions can include selecting the first subsetof optical subcarriers from the first portion of the modulated opticalsignal, selecting the second subset of subcarriers from the secondportion of the modulated optical signal, transmitting the first subsetof optical subcarriers to the second network device using the firstcommunications link, and transmitting the second subset of opticalsubcarriers to the second network device using the second communicationslink. Example components for performing these actions are shown, forinstance, in FIGS. 4A and 4B.

In some implementations, selecting the first subset of opticalsubcarriers can include selecting the first subset of opticalsubcarriers with a wavelength selective switch (e.g., as shown in FIGS.4A and 4B. In some implementations, selecting the second subset ofoptical subcarriers can include selecting the second subset of opticalsubcarriers with the wavelength selective switch (e.g., as shown inFIGS. 4A and 4B).

FIG. 16B shows another example process 1610 that can be performed usingone or more of the systems described herein. For instance, the 1610 canbe performed using an optical communications network 100 and/or one ormore of the components thereof (e.g., as shown in FIGS. 1-15 ).

According to the process 1610, a first network device and a secondnetwork device receive data to be transmitted to a third network deviceover an optical communications network (block 1612).

In some implementations, each of the first network device and the secondnetwork device can include one or more hub network devices. Further, thethird network device can include one or more leaf network devices. As anexample, referring to FIG. 8 , the first network device can include thenode 104 a, and the second network device can include the node 104 b. Asanother example, the second network device can include one of the nodes106 a-106 p.

The first network device transmits, to the third network device, firstinformation indicative of the data using a first communications link ofthe optical communications network (block 1614). The first informationis transmitted using a first subset of optical subcarriers; and

The second network device transmits, to the third network device, secondinformation indicative of the data using a second communications link ofthe optical communications network (block 1616). The second informationis transmitted using a second subset of optical subcarriers. Further,the first subset of optical subcarriers is different from the secondsubset of optical subcarriers.

In some implementations, the first information and the secondinformation can be identical. In some implementations, the firstinformation can be different from the second information. For example,the first information and the second information can include the samedata modulated according to different digital subcarriers. As anotherexample, the first information and the second information can includethe same data transmitted according to different forward errorcorrection (FEC) schemes (e.g., include different FEC codes or bits).

In some implementations, the first communications link and the secondcommunications link can form at least a portion of a communications ringthat communicatively interconnects the first network device, the secondnetwork device, and the third network device. As an example, referringto FIG. 8 , the first communications link can include at least a portionof the optical path 108 a, and the second communications link caninclude at least a portion of the optical path 108 b, or vice versa. Insome implementations, the first communications link can be referred toas a “hub working Tx” path, and the second communications link can bereferred to as a “hub protect Tx” path, or vice versa.

In some implementations, each of the optical subcarriers in the firstsubset of optical subcarriers and the second subset of opticalsubcarriers can be a respective Nyquist subcarrier. Further, in someimplementations, each of the optical subcarriers are associated withrespective frequencies that do not overlap one another in a frequencydomain.

In some implementations, the first subset of optical subcarriers can beselected from a plurality of optical subcarriers allotted to the firstnetwork device. For example, the first network device can be allottedsubcarriers S1-SC16 for use in communicating over an opticalcommunications network. The first subset can be selected from among thesubcarriers SC1-SC16.

In some implementations, the optical subcarriers of the first subset ofoptical subcarriers can be associated with respective frequencies thatare contiguous with one another in a frequency domain. As an example,the first subset of optical subcarriers can be SC1 and SC2.

In some implementations, the second subset of optical subcarriers can beselected from the plurality of optical subcarriers allotted to thesecond network device. For example, the second network device can beallotted subcarriers S17-SC32 for use in communicating over an opticalcommunications network. The second subset can be selected from among thesubcarriers SC17-SC32.

In some implementations, the optical subcarriers of the second subset ofoptical subcarriers are associated with respective frequencies that arecontiguous with one another in a frequency domain. As an example, thesecond subset of optical subcarriers can be SC9 and SC10.

In some implementations, the first subset of optical subcarriers can beassociated with one or more first frequencies, and the second subset ofoptical subcarriers can be associated with one or more secondfrequencies. In some implementations, the one or more first frequenciesare not contiguous with the one or more second frequencies in afrequency domain. As an example, the first subset of optical subcarrierscan be SC1, and the second subset of optical subcarriers can be SC17.

In some implementations, the first subset of optical subcarriers can beassociated with one or more first frequencies, the second subset ofoptical subcarriers can be associated with one or more secondfrequencies, and one or more additional optical subcarriers can beassociated with one or more additional frequencies. The one or moreadditional frequencies can be disposed between the one or more firstfrequencies and the one or more second frequencies in a frequencydomain. As an example, the first subset of optical subcarriers can beSC1-SC4, and the second subset of optical subcarriers can be SC29-SC32,with the additional optical subcarriers SC5-SC28 disposed between themin the frequency domain.

In some implementations, the first subset of optical subcarriers can beassociated with one or more first frequencies, and the second subset ofoptical subcarriers can be associated with one or more secondfrequencies. Further, the one or more first frequencies and the one ormore second frequencies can be separated from one another by one or moreadditional frequencies in a frequency domain. As an example, a guardband (e.g., a frequency band spanning a range of frequencies) canseparate the one or more first frequencies and the one or more secondfrequencies from one another.

In some implementations, a number of optical subcarriers in the firstsubset of optical subcarriers can be the same as a number of opticalsubcarriers in the second subset of optical subcarriers. For example,the first subset of optical subcarriers can be SC1, and the secondsubset of optical subcarriers can be SC17.

In some implementations, a number of optical subcarriers in the firstsubset of optical subcarriers can be different from a number of opticalsubcarriers in the second subset of optical subcarriers. For example,the first subset of optical subcarriers can be SC1 and SC2, and thesecond subset of optical subcarriers can be SC17.

In some implementations, transmitting the first information can includemodulating, by the first network device, an output of a first laser togenerate a first modulated optical signal including the first subset ofoptical subcarriers. Further, the first modulated optical signal can betransmitted to the third network device using the first communicationslink. Example components for performing these actions are shown, forinstance, in FIG. 9 .

In some implementations, transmitting the second information can includemodulating, by the second network device, an output of a second laser togenerate a second modulated optical signal including the second subsetof optical subcarriers. Further, the second modulated optical signal canbe transmitted to the third network device using the firstcommunications link. Example components for performing these actions areshown, for instance, in FIG. 9 .

FIG. 16C shows another example process 1620 that can be performed usingone or more of the systems described herein. For instance, the 1620 canbe performed using an optical communications network 100 and/or one ormore of the components thereof (e.g., as shown in FIGS. 1-15 ).

According to the process 1620, a first network device receives data tobe transmitted to a second network device over an optical communicationsnetwork (block 1622).

The first network device transmits, to the second device, firstinformation indicative of the data using a first communications link ofthe optical communications network (block 1624). The first informationis transmitted using a first subset of optical subcarriers.

In some implementations, the first network device can include one ormore hub network devices, the second network device can include one ormore leaf network devices, or vice versa. As an example, the firstnetwork device can include the node 104. As another example, the secondnetwork device can include one of the nodes 106 a-106 n.

The first network device determines a fault in the first communicationslink (block 1626).

In some implementations, determining the fault in the firstcommunications link can include determining that an optical fiber of thefirst communications link has been severed and/or determining that aline system component of the first communications link ismalfunctioning.

In response, the first network device transmits second informationindicative of the data using a second communications link of the opticalcommunications network (block 1628). The second information istransmitted using a second subset of optical subcarriers. The firstsubset of optical subcarriers is different from the second subset ofoptical subcarriers.

In some implementations, the first information and the secondinformation can be identical. For example, the first information and thesecond information both can into the data modulated according to thesame digital subcarrier or subcarriers. In some implementations, thefirst information can be different from the second information. Forexample, the first information and the second information can includethe same data modulated according to different digital subcarriers. Asanother example, the first information and the second information caninclude the same data transmitted according to different forward errorcorrection (FEC) schemes (e.g., include different FEC codes or bits).

In some implementations, the first communications link and the secondcommunications link can form at least a portion of a communications ringthat communicatively interconnects the first network device, the secondnetwork device, and the third network device. As an example, referringto FIG. 8 , the first communications link can include at least a portionof the optical path 108 a, and the second communications link caninclude at least a portion of the optical path 108 b, or vice versa. Insome implementations, the first communications link can be referred toas a “hub working Tx” path, and the second communications link can bereferred to as a “hub protect Tx” path, or vice versa.

In some implementations, each of the optical subcarriers in the firstsubset of optical subcarriers and the second subset of opticalsubcarriers can be a respective Nyquist subcarrier. Further, in someimplementations, each of the optical subcarriers are associated withrespective frequencies that do not overlap one another in a frequencydomain.

In some implementations, the first subset of optical subcarriers can beselected from a plurality of optical subcarriers allotted to the firstnetwork device. For example, the first network device can be allottedsubcarriers S1-SC16 for use in communicating over an opticalcommunications network. The first subset can be selected from among thesubcarriers SC1-SC16.

In some implementations, the optical subcarriers of the first subset ofoptical subcarriers can be associated with respective frequencies thatare contiguous with one another in a frequency domain. As an example,the first subset of optical subcarriers can be SC1 and SC2.

In some implementations, the optical subcarriers of the first subset ofoptical subcarriers are associated with respective frequencies that arecontiguous with one another in a frequency domain. As an example,referring to FIG. 3 , the first subset of optical subcarriers can be SC1and SC2.

In some implementations, the second subset of optical subcarriers can beselected from the plurality of optical subcarriers allotted to the firstnetwork device. For example, referring to FIG. 3 , the first networkdevice can be allotted one or more of the subcarriers S1-SC16 for use incommunicating over an optical communications network (e.g., fortransmitting data over the optical communications network). The secondsubset can be selected from among the subcarriers SC1-SC16.

In some implementations, the optical subcarriers of the second subset ofoptical subcarriers can be associated with respective frequencies thatare contiguous with one another in a frequency domain. As an example,referring to FIG. 3 , the second subset of optical subcarriers can beSC9 and SC10.

In some implementations, the first subset of optical subcarriers can beassociated with one or more first frequencies, and the second subset ofoptical subcarriers can be associated with one or more secondfrequencies. In some implementations, the one or more first frequenciesare not contiguous with the one or more second frequencies in afrequency domain. As an example, referring to FIG. 3 , the first subsetof optical subcarriers can be SC1, and the second subset of opticalsubcarriers can be SC9.

In some implementations, the first subset of optical subcarriers can beassociated with one or more first frequencies, and the second subset ofoptical subcarriers can be associated with one or more secondfrequencies. Further, one or more additional optical subcarriers can beassociated with one or more additional frequencies. Further, the one ormore additional frequencies can be disposed between the one or morefirst frequencies and the one or more second frequencies in a frequencydomain. As an example, referring to FIG. 3 , the first subset of opticalsubcarriers can be SC1-SC4, and the second subset of optical subcarrierscan be SC13-SC16, with the additional optical subcarriers SC5-SC12disposed between them in the frequency domain.

In some implementations, the first subset of optical subcarriers can beassociated with one or more first frequencies, and the second subset ofoptical subcarriers can be associated with one or more secondfrequencies. Further, the one or more first frequencies and the one ormore second frequencies can be separated from one another by one or moreadditional frequencies in a frequency domain. As an example, referringto FIG. 3 , a guard band (e.g., a frequency band spanning a range offrequencies) can separate the one or more first frequencies and the oneor more second frequencies from one another.

In some implementations, a number of optical subcarriers in the firstsubset of optical subcarriers can be the same as a number of opticalsubcarriers in the second subset of optical subcarriers. For example,referring to FIG. 3 , the first subset of optical subcarriers can beSC1, and the second subset of optical subcarriers can be SC9.

In some implementations, a number of optical subcarriers in the firstsubset of optical subcarriers can be different from a number of opticalsubcarriers in the second subset of optical subcarriers. For example,referring to FIG. 3 , the first subset of optical subcarriers can be SC1and SC2, and the second subset of optical subcarriers can be SC9.

FIG. 16D shows another example process 1630 that can be performed usingone or more of the systems described herein. For instance, the 1630 canbe performed using an optical communications network 100 and/or one ormore of the components thereof (e.g., as shown in FIGS. 1-15 ).

In some implementations, the first network device can include one ormore hub network devices, and the second network device can include oneor more leaf network devices, or vice versa. As an example, the firstnetwork device can include the node 104. As another example, the secondnetwork device can include one of the nodes 106 a-106 n.

According to the process 1630, a first network device monitors forincoming optical signals on a first communications link and a secondcommunications link of an optical communications network (block 1632).Each of the first communications link and the second communications linkcommunicatively interconnects the first network device and a secondnetwork device.

The first network device receives at least one of a first signal or asecond signal (block 1634). The first signal includes first informationindicative of data transmitted by the second network device using thefirst communications link and using a first subset of opticalsubcarriers. The second signal includes second information indicative ofthe data transmitted by the second network device using the secondcommunications link and using a second subset of optical subcarriers.The first subset of optical subcarriers is different from the secondsubset of optical subcarriers.

The first network device retrieves the data from at least one of thefirst signal or the second signal (block 1636).

In some implementations, the process 1630 can also include transmittingthe data to a third network device and/or transmitting the data to thethird network device.

In some implementations, the first communications link and the secondcommunications link can form at least a portion of a communications ringthat communicatively interconnects the first network device and thesecond network device. As an example, referring to FIG. 1A, the firstcommunications link can include at least a portion of the optical path108 a, and the second communications link can include at least a portionof the optical path 108 b, or vice versa. In some implementations, thefirst communications link can be referred to as a “hub working Tx” path,and the second communications link can be referred to as a “hub protectTx” path, or vice versa.

In some implementations, each of the optical subcarriers in the firstsubset of optical subcarriers and the second subset of opticalsubcarriers can be a respective Nyquist subcarrier. Further, in someimplementations, each of the optical subcarriers are associated withrespective frequencies that do not overlap one another in a frequencydomain.

In some implementations, the optical subcarriers of the first subset ofoptical subcarriers are associated with respective frequencies that arecontiguous with one another in a frequency domain. As an example,referring to FIG. 3 , the first subset of optical subcarriers can be SC1and SC2.

In some implementations, the optical subcarriers of the second subset ofoptical subcarriers can be associated with respective frequencies thatare contiguous with one another in a frequency domain. As an example,referring to FIG. 3 , the second subset of optical subcarriers can beSC9 and SC10.

In some implementations, the first frequencies are not contiguous withthe second frequencies in the frequency domain. As an example, referringto FIG. 3 , the first subset of optical subcarriers can be SC1, and thesecond subset of optical subcarriers can be SC9.

In some implementations, one or more additional optical subcarriers canbe associated with one or more additional frequencies, and the one ormore additional frequencies can be disposed between the one or morefirst frequencies and the one or more second frequencies in thefrequency domain. As an example, referring to FIG. 3 , the first subsetof optical subcarriers can be SC1-SC4, and the second subset of opticalsubcarriers can be SC13-SC16, with the additional optical subcarriersSC5-SC12 disposed between them in the frequency domain.

In some implementations, the first subset of optical subcarriers can beassociated with one or more first frequencies, and the second subset ofoptical subcarriers can be associated with one or more secondfrequencies. Further, the one or more first frequencies and the one ormore second frequencies can be separated from one another by one or moreadditional frequencies in the frequency domain. As an example, referringto FIG. 3 , a guard band (e.g., a frequency band spanning a range offrequencies) can separate the one or more first frequencies and the oneor more second frequencies from one another.

In some implementations, a number of optical subcarriers in the firstsubset of optical subcarriers can be the same as a number of opticalsubcarriers in the second subset of optical subcarriers. For example,referring to FIG. 3 , the first subset of optical subcarriers can beSC1, and the second subset of optical subcarriers can be SC9.

In some implementations, data can be retrieved from at least one of thefirst signal or the second signal by performing one or more particularactions. The actions can include determining, by the first networkdevice, that the first signal was not received from the second networkdevice, and determining, by the first network device, that the secondsignal was received from the second network device. The actions can alsoinclude, responsive to these two determinations, retrieving, by thefirst network device, the data from the second signal.

In some implementations, monitoring for incoming optical signals on thefirst communications link and the second communications link can includetuning a receiver of the first network device to one or more firstfrequencies associated with the first subset of optical subcarriers, andin response to determining that the first signal was not received fromthe second network device, tuning the receiver of the first networkdevice to one or more second frequencies associated with the secondsubset of optical subcarriers.

In some implementations, the data can be retrieved from at least one ofthe first signal or the second signal by performing one or moreparticular actions. The actions can include determining, by the firstnetwork device, that the first signal was received from the secondnetwork device, and determining, by the first network device, one ormore first quality metrics associated with the first signal. The firstquality metrics can include an indication of a latency associated with atransmission of the first signal using the first communications linkand/or an indication of a pre-forward error correction quality factor(pre-FEC Q) associated with a transmission of the first signal using thefirst communications link.

The actions can also include determining, by the first network device,that the second signal was received from the second network device, anddetermining, by the first network device, one or more second qualitymetrics associated with the second signal. The second quality metricscan include an indication of a latency associated with a transmission ofthe second signal using the second communications link and/or anindication of a forward error correction quality factor (pre-FEC Q)associated with a transmission of the second signal using the secondcommunications link.

The action can also include retrieving, based on the one or more firstquality metrics and the one or more second quality metrics, the datafrom one of the first signal or the second signal.

III. Example Computer Systems

Some implementations of subject matter and operations described in thisspecification can be implemented in digital electronic circuitry, or incomputer software, firmware, or hardware, including the structuresdisclosed in this specification and their structural equivalents, or incombinations of one or more of them. For example, in someimplementations, some or all of the components described herein can beimplemented using digital electronic circuitry, or in computer software,firmware, or hardware, or in combinations of one or more of them. Inanother example, the process ### can be implemented using digitalelectronic circuitry, or in computer software, firmware, or hardware, orin combinations of one or more of them.

Some implementations described in this specification can be implementedas one or more groups or modules of digital electronic circuitry,computer software, firmware, or hardware, or in combinations of one ormore of them. Although different modules can be used, each module neednot be distinct, and multiple modules can be implemented on the samedigital electronic circuitry, computer software, firmware, or hardware,or combination thereof.

Some implementations described in this specification can be implementedas one or more computer programs, i.e., one or more modules of computerprogram instructions, encoded on computer storage medium for executionby, or to control the operation of, data processing apparatus. Acomputer storage medium can be, or can be included in, acomputer-readable storage device, a computer-readable storage substrate,a random or serial access memory array or device, or a combination ofone or more of them. Moreover, while a computer storage medium is not apropagated signal, a computer storage medium can be a source ordestination of computer program instructions encoded in an artificiallygenerated propagated signal. The computer storage medium also can be, orcan be included in, one or more separate physical components or media(e.g., multiple CDs, disks, or other storage devices).

The term “data processing apparatus” encompasses all kinds of apparatus,devices, and machines for processing data, including by way of example aprogrammable processor, a computer, a system on a chip, or multipleones, or combinations, of the foregoing. The apparatus can includespecial purpose logic circuitry, e.g., an FPGA (field programmable gatearray) or an ASIC (application specific integrated circuit). Theapparatus also can include, in addition to hardware, code that createsan execution environment for the computer program in question, e.g.,code that constitutes processor firmware, a protocol stack, a databasemanagement system, an operating system, a cross-platform runtimeenvironment, a virtual machine, or a combination of one or more of them.The apparatus and execution environment can realize various differentcomputing model infrastructures, such as web services, distributedcomputing and grid computing infrastructures.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, declarative orprocedural languages. A computer program may, but need not, correspondto a file in a file system. A program can be stored in a portion of afile that holds other programs or data (e.g., one or more scripts storedin a markup language document), in a single file dedicated to theprogram in question, or in multiple coordinated files (e.g., files thatstore one or more modules, sub programs, or portions of code). Acomputer program can be deployed to be executed on one computer or onmultiple computers that are located at one site or distributed acrossmultiple sites and interconnected by a communication network.

Some of the processes and logic flows described in this specificationcan be performed by one or more programmable processors executing one ormore computer programs to perform actions by operating on input data andgenerating output. The processes and logic flows also can be performedby, and apparatus also can be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andprocessors of any kind of digital computer. Generally, a processor willreceive instructions and data from a read only memory or a random accessmemory or both. A computer includes a processor for performing actionsin accordance with instructions and one or more memory devices forstoring instructions and data. A computer may also include, or beoperatively coupled to receive data from or transfer data to, or both,one or more mass storage devices for storing data, e.g., magnetic,magneto optical disks, or optical disks. However, a computer need nothave such devices. Devices suitable for storing computer programinstructions and data include all forms of non-volatile memory, mediaand memory devices, including by way of example semiconductor memorydevices (e.g., EPROM, EEPROM, flash memory devices, and others),magnetic disks (e.g., internal hard disks, removable disks, and others),magneto optical disks, and CD-ROM and DVD-ROM disks. The processor andthe memory can be supplemented by, or incorporated in, special purposelogic circuitry.

A computer system may include a single computing device, or multiplecomputers that operate in proximity or generally remote from each otherand typically interact through a communication network. Examples ofcommunication networks include a local area network (“LAN”) and a widearea network (“WAN”), an inter-network (e.g., the Internet), a networkcomprising a satellite link, and peer-to-peer networks (e.g., ad hocpeer-to-peer networks). A relationship of client and server may arise byvirtue of computer programs running on the respective computers andhaving a client-server relationship to each other.

FIG. 17 shows an example computer system 1700 that includes a processor1710, a memory 1720, a storage device 1730 and an input/output device1740. Each of the components 1710, 1720, 1730 and 1740 can beinterconnected, for example, by a system bus 1750. The processor 1710 iscapable of processing instructions for execution within the system 1700.In some implementations, the processor 1710 is a single-threadedprocessor, a multi-threaded processor, or another type of processor. Theprocessor 1710 is capable of processing instructions stored in thememory 1720 or on the storage device 1730. The memory 1720 and thestorage device 1730 can store information within the system 1700.

The input/output device 1740 provides input/output operations for thesystem 1700. In some implementations, the input/output device 1740 caninclude one or more of a network interface device, e.g., an Ethernetcard, a serial communication device, e.g., an RS-232 port, and/or awireless interface device, e.g., an 802.11 card, a 3G wireless modem, a4G wireless modem, a 5G wireless modem, etc. for communicating with anetwork 1770 (e.g., via one or more network devices, such as switches,routers, and/or other network devices). In some implementations, theinput/output device can include driver devices configured to receiveinput data and send output data to other input/output devices, e.g.,keyboard, printer and display devices 1760. In some implementations,mobile computing devices, mobile communication devices, and otherdevices can be used.

While this specification contains many details, these should not beconstrued as limitations on the scope of what may be claimed, but ratheras descriptions of features specific to particular examples. Certainfeatures that are described in this specification in the context ofseparate implementations also can be combined in the sameimplementation. Conversely, various features that are described in thecontext of a single implementation also can be implemented in multipleembodiments separately or in any suitable sub-combination.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made without departingfrom the spirit and scope of the invention. Accordingly, otherimplementations are within the scope of the claims.

What is claimed is:
 1. A system comprising: a first network devicecomprising: first circuitry, wherein the first network device isconfigured to perform operations comprising: receiving data to betransmitted to a second network device over an optical communicationsnetwork, transmitting, to the second device, first informationindicative of the data using a first communications link of the opticalcommunications network, wherein the first information is transmittedusing a first subset of optical subcarriers, determining a fault in thefirst communications link, and responsive to determining the fault inthe first communications link, transmitting, to the second networkdevice, second information indicative of the data using a secondcommunications link of the optical communications network, wherein thesecond information is transmitted using a second subset of opticalsubcarriers, and wherein the first subset of optical subcarriers isdifferent from the second subset of optical subcarriers; and atransmitter comprising a laser and a modulator, the modulator receivinglight from the laser and modulating said light to output the first andsecond subsets of optical subcarriers, such that the first subset of theplurality of optical subcarriers output from the modulator carries thefirst information and the second subset of optical subcarriers carriesthe second information, and the first subset of optical subcarriers andthe second subset of optical subcarriers are associated with the laserand each of the plurality of optical subcarriers do not spectrallyoverlap with one another.
 2. The system of claim 1, wherein the firstnetwork device is configured to determine the fault in the firstcommunications link by: determining that an optical fiber of the firstcommunications link has been severed.
 3. The system of claim 1, whereinthe first network device is configured to determine the fault in thefirst communications link by: determining that a line system componentof the first communications link is malfunctioning.
 4. The system ofclaim 1, wherein the first information and the second information areidentical.
 5. The system of claim 1, wherein the first information isdifferent from the second information.
 6. The system of claim 1, whereinthe first communications link and the second communications link form atleast a portion of a communications ring that communicativelyinterconnects the first network device and the second network device. 7.The system of claim 1, wherein the first subset of optical subcarriersis selected from a plurality of optical subcarriers allotted to thefirst network device.
 8. The system of claim 7, wherein the opticalsubcarriers of the first subset of optical subcarriers are associatedwith respective frequencies that are contiguous with one another in afrequency domain.
 9. The system of claim 7, wherein the second subset ofoptical subcarriers is selected from the plurality of opticalsubcarriers allotted to the first network device.
 10. The system ofclaim 9, wherein the optical subcarriers of the second subset of opticalsubcarriers are associated with respective frequencies that arecontiguous with one another in a frequency domain.
 11. The system ofclaim 9, wherein the first subset of optical subcarriers is associatedwith one or more first frequencies, wherein the second subset of opticalsubcarriers is associated with one or more second frequencies, andwherein the one or more first frequencies are not contiguous with theone or more second frequencies in a frequency domain.
 12. The system ofclaim 9, wherein the first subset of optical subcarriers is associatedwith one or more first frequencies, wherein the second subset of opticalsubcarriers is associated with one or more second frequencies, whereinone or more additional optical subcarriers are associated with one ormore additional frequencies, and wherein the one or more additionalfrequencies are disposed between the one or more first frequencies andthe one or more second frequencies in a frequency domain.
 13. The systemof claim 9, wherein the first subset of optical subcarriers isassociated with one or more first frequencies, wherein the second subsetof optical subcarriers is associated with one or more secondfrequencies, and wherein the one or more first frequencies and the oneor more second frequencies are separated from one another by one or moreadditional frequencies in a frequency domain.
 14. The system of claim 1,wherein a number of optical subcarriers in the first subset of opticalsubcarriers is the same as a number of optical subcarriers in the secondsubset of optical subcarriers.
 15. The system of claim 1, wherein anumber of optical subcarriers in the first subset of optical subcarriersis different from a number of optical subcarriers in the second subsetof optical subcarriers.
 16. The system of claim 1, wherein the firstnetwork device comprises one or more hub network devices, and whereinthe second network device comprise one or more leaf network devices. 17.The system of claim 1, wherein each of the optical subcarriers in thefirst subset of optical subcarriers and the second subset of opticalsubcarriers is a respective Nyquist subcarrier.
 18. The system of claim1, wherein the first subset of optical subcarriers is transmitted alonga working path and the second subset of optical subcarriers istransmitted along a working path.